Abulia Lack of will, lack of impulse, inability to make decision. See frontal lobe abulia.

Accommodation reflex. 3-part reflex brought into action by looking at a near object: the eyes turn inward, the pupils constrict and the ciliary muscles relax resulting in thickening of the lens.

Adiadochokinesis. Inability to perform rapid alternating movements such as pronation-supination of the forearm or successive touching of each finger to the thumb. This symptom suggests damage to the cerebellum or its connections. (Synonym dysdiadochokinesis)

Agnosia. The inability to recognize an object despite having basic sensory abilities (vision, hearing, touch and language functions, etc.) intact. There are many types of agnosia, for example see finger agnosia.

Agraphia. (also called anorthography) The inability to write language. Pure agraphia without disturbance of other language functions is rare.

Agraphesthesia. Inability to identify a number or letter written on the hand (or other part of the body). Graphesthesia requires intact epicritic perception.

Alexia. The inability to understand written language.

Amaurosis fugax. An episode of abrupt, temporary monocular blindness (or blurring of vision) caused by transient retinal ischemia.

Amnesia. Loss of memory. See anterograde amnesia and retrograde anmesia

Amyloid. An adjective meaning "starch-like." Also used as a noun to refer to a protein-polysaccharide complex that forms deposits in organs and vessels.

Amyloid angiopathy. Cause of vascular degeneration in which a protein-polysaccharide complex deposits within blood vessels. Such vessels are more prone to hemorrhage. This condition is more likely to be found among the elderly and is associated with lobar hemorrhage.

Amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig's disease). A "system" disease of slow onset involving destruction of both upper and lower motor neurons.

Anencephaly. Congenital absence of forebrain and calvaria due to failure of fusion of the neural plate.

Aneurysm. Local dilation ("ballooning") of an artery due to a weakening of the arterial wall. In large vessels, the mechanism which weakens the wall is almost always atherosclerosis.

Angiography. Radiographic technique for imaging blood vessels.  In classic methods, the vessels of the brain are visualized by injection of radiopaque dye. Digital subtraction angiography (using computer processing to produce images) carries less risk for the patient because the amount of dye can be reduced. Magnetic resonance angiography is a newer, noninvasive technique that is helpful for visualizing extracranial and large intracranial vessles.  However, at present, invasive angiograpy is more sensitive for smaller vessels.

Anisocoria. Pupillary asymmetry. Most people have pupils equal in size; however, mild asymmetry can be normal.

Anorthography. See agraphia.

Anosmia. Loss of sense of smell. Not routinely tested in neurological exam (though it probably should be) unless patient complains of loss of smell or taste. Usually caused by nasal inflammation but can be caused by trauma or tumor of the orbital frontal lobe.

Anosognosia. Patient is unaware that anything is wrong with them. Often accompanies unilateral neglect following a right parietal lobe lesion.

Anterior circulation. The internal carotid artery and its branches.

Anterograde amnesia. Loss of memory of events occurring after onset of amnesia, inability to form new memories. Anterograde amnesia is the key component of Korsakoff's "psychosis".

Aphasia. A loss or impairment of the production and/or understanding of written or spoken language. Aphasia is an intellectual impairment, and is quite different from the purely motor problems of dysarthria.

Apraxia. Inability to perform familiar movements despite absence of paralysis or sensory deficit. See dressing apraxia.

Arteriography. Radiographic technique for imaging arteries. See angiography.

Arteriosclerosis. Hardening and thickening of arterial walls due to pathologic changes in the intima and/or media.

Arteriovenous malformation. Abbreviated AVM; congenitally abnormal arteries and/or veins.

Astereognosis. Inability to identify, by touch alone, objects placed in the hand such as differentiating between a dime and a quarter.

Ataxia. Incoordination of voluntary movement. It is a sign of damage to pathways connecting the cerebellum with the spinal cord and brainstem, or damage to parts of the cerebellum itself.

Atherosclerosis. A disease of large- and medium-sized arteries in which the intima (the layer of the arterial wall closest to the lumen) accumulates abnormal patches of lipids and cells that eventually expand to form elevated 'plaques' which can obstruct blood flow.  Established plaques can undergo a series of additional events that increase the patient's chances of serious vascular complications.  For example, plaques may ulcerate and promote thrombus formation; they may break open and shed emboli; they may calcify and further stiffen the vessel wall; they may cause rupture of the entire arterial wall leading to hemorrhage.

Athetosis. Involuntary slow, sinuous movements. They may alternate smoothly between extension-pronation and flexion-suppination of the arm or between eversion and inversion of the foot, to cite just two possible examples. Seen after damage to the striatum.

Athlete's high. A reduction in perception of pain by sustained, intense concentration of mind and body on a physically and mentally demanding activity.

Auscultation The diagnostic technique of listening to sounds within the body, usually to ascertain the condition of blood vessels and thoracic or abdominal viscera.  A stethoscope is often used.

Babinski sign. An abnormal (dorsiflexor) plantar reflex.

Bell's palsy. Paralysis of all muscles of facial expression (corner of mouth droops, palpebral fissure is widened, forehead is unfurrowed) which has a sudden onset. It is due to lesion of the VIIth nerve, and may be accompanied by loss of taste sensation, and reduced salivation and lacrimation depending on exactly which components are involved. Causation is unclear. About 90% of patients have only demyelination of the nerve, and recover in a few weeks; a longer recovery period is required if axon degeneration has occurred. Axon regeneration may take over a year, and is often incomplete.

Binasal hemianopsia. A rare heteronymous hemianopsia that could occur in the unlikely event that there are aneurysms of both internal carotid arteries at the level of the optic chiasm thus compressing the chiasm laterally. See visual field defects.

Bitemporal hemianopsia. A heternomymous hemianopsia consisting of loss of vision in the temporal visual fields usually caused by damage to the central portion of the optic chiasm. See visual field defects.

Broca's aphasia. (Synonyms: anterior, expressive, or nonfluent aphasia). A primary deficit in language output (production), in which comprehension is largely unaffected. The defect may involve loss of all propositional speech, or the patient may use a small number of substantive words which are laboriously enunciated and not combined into grammatical phrases. The patient can repeat words, but the repetition has the same abnormalities as the individuals' own speech. The impairment in writing is usually equally severe. The patient is almost always aware of the problem. In right-handers, the lesion is in the left inferior frontal lobe; often there is accompanying paralysis of the lower face or arm on the right side.

Brown-Sequard syndrome. A set of findings that may be produced by incomplete or complete hemisection (damage to one side) of the spinal cord: 1) Ipsilateral upper motor neuron paralysis involving muscles innervated by segments below the lesion. 2) Ipsilateral lower motor neuron paralysis involving muscles innervated by the damaged segments. 3) Contralateral loss of pain and temperature sensation beginning several segments below the level of lesion. 4) Ipsilateral loss of two-point discrimination and joint position sense below the level of lesion. 5) Anesthesia to all sensations in dermatomes supplied by the damaged segments.

Bruit. A sound or murmur, often abnormal, heard during auscultation.  For example, the presence of severe stenosis of the carotid artery in the neck may produce a bruit by causing turbulent blood flow.

Caloric nystagmus. Nystagmus elicited by instilling warm or cool water into one ear canal. This is a normal physiological response, and is an important clinical test for the integrity of the membraneous labyrinth, and vestibular components of the VIIIth nerve.

Cerebral palsy. A general term sometimes applied to motor abnormalities that have their onset early in life. It is a catch-all phrase, and encompasses a variety of diseases that occur before, at, or in the first months after birth.

Chorea. Involuntary rapid, jerky movements. Seen after damage to the striatum.

Choreoathetosis. Involuntary movements with features of both chorea and athetosis. These two movement patterns have many similarities, and even the experts often use this combined term. Seen after damage to the striatum.

Chromophobe adenoma. A benign epithelial tumor of a subset of cells in the anterior lobe of the pituitary. See pituitary tumor.

Circumlocution. A roundabout, indirect or lengthy way of speaking.

Clasp-knife phenomenon. Description of the abnormal way that paralyzed limb muscles respond to passive stretch after pyramidal tract damage. Characteristically, the greater the velocity of stretch, the greater the resistance of the muscle.

Clonus. An abnormal response to the stretching of a muscle. It consists of a series of rhythmic involunary muscle contractions that occur in response to a single stretch, such as tapping the tendon to elicit a muscle stretch reflex.

Coma. A state in which patient is incapable of being aroused by external stimuli or inner needs.Can be characterized by absence of sleep/wake cycles and loss of response to even vigorous stimulation. Compare to "locked-in state" in which there is little or no disturbance of awareness (consciousness) but only an inability of the patient to respond to stimuli.

Conduction aphasia. A deficit in language in which comprehension of language is preserved, but the individual's speech is defective in ways resembling Wernicke's aphasia: fluent, properly articulated, but largely nonsensical. The patient is aware of the problem, but is unable to correct his or her own erroneous speech. This syndrome occurs when the anterior and posterior speech areas are both intact but are disconnected from each other because of a lesion in the arcuate fasciculus on the left side.

Confabulate (fabricate). To fill in gaps in memories with fabricated facts which he/she believes to be true. Confabulation is often seen in Korsakoff's "psychosis" and lesions involving the hippocampus.

Conjugate gaze. The symmetrical and synchronous movement of the eyes (from Latin conjugatus, yoked or joined together.)


Convergent gaze. Simultaneous movements of the eyes toward the midline. They are required to fuse the visual images by keeping the images focused on corresponding parts of the retinas. This is essential for near vision.. When we look at near objects, three things occur: turning of the eyes inward, constriction of the pupils, and relaxation of the ciliary muscles to allow the lens to thicken. Collectively, this triad is referred to as accomodation. See accommodation reflex.

Corneal reflex. Light touch on the cornea produces closure of that eye (a blink), or closure of both eyes if the stimulus is more intense. Afferent limb of reflex involves trigeminal ganglion cells whose distal axon branches run in the ophthalmic division of V and central branches which enter the descending tract of V and synapse with cells in the interpolar part of the spinal nucleus. Eventually motoneurons in the VIIth nucleus are activated, and they in turn produce contraction of the orbicularis oculi. (Note that the corneal reflex does not involve the upper lid, which is controlled by the IIIrd nerve.)

Corticobulbar tract disease (supranuclear facial weakness) Results in paralysis of the facial muscles contralateral to the lesion with sparing of the forehead. Thus patients with supranuclear facial weakness can raise their eyebrows because motoneurons to forehead are bilaterally innervated by the corticobulbar tract whereas motoneurons to the rest of the facial muscles are innervated by the contralateral cortex. Contrast with Bell's Palsy.

Craniopharyngioma. Benign tumors generally believed to originate from remnants of Rathke's pouch at the junction of the infundibular stalk and pituitary. Usually lies above the sella turcica and can affect the optic chiasm, pituitary and hypthalamus.

Crossed extension. Reflex seen when several segments of spinal cord are intact bilaterally. When stimulated with active flexion of one limb the opposite limb extends. This reflex serves the purpose of stabilizing the organism when one limb is withdrawn as in the withdrawal reflex.

Crossed motor impairment. A pattern of motor impairment produced by brainstem lesions (i.e., lesions rostral to the pyramidal decussation) in which there is upper motor neuron paralysis of the arm and leg contralateral to the lesion, and lower motor neuron paralysis involving a cranial nerve motor function ipsilateral to the lesion. Also called crossed weakness.

Crossed pain and temperature loss. Loss of pain and temperature sensation on one side of the face, and the opposite side of the body. This can be produced by lateral lesions in the caudal pons or medulla which damage EITHER the descending (spinal) tract of V or the caudal part of the spinal nucleus of V AND the spinothalamic tract. By contrast, single lesions in the rostral pons or midbrain usually produce contralateral loss of pain and temperature in both face and body, since the part of the trigeminal system present at these rostral levels (second-order trigeminothalamic fibers) is mostly crossed.

Crude light touch. The ability to indicate that an object is touching the body surface, but without a precise localization, hence crude. When crude light touch is impaired, the threshold for touch sensation is usually elevated. Many synonyms are used: simple touch, elementary touch, crude touch, or light touch.

Decerebrate rigidity (pontine extensor rigidity, positive supporting reflex) stimulation of plantar surface of one or more limbs leads to extension of all four limbs. Most likely mediated by the lateral vestibulospinal tract at the level of the pons.

Decorticate postures. Refex postures of limbs of a paralyzed or obtunded patient, mediated at the level of the red nucleus and more complex than decerebrate rigidity. The commonest form is extension of the leg(s) accompanied by flexion of the arm(s). See Magnus Dekleijn reflex and red nucleus walking.

Deep tendon reflexes. See stretch reflexes.

Dementia. A condition in which intellectual or cognitive functions deteriorate, with little disturbance of consciousness. Usually the intellectual failure is accompanied by changes in behavior or personality. Dementia can be caused by cerebral atrophy (mainly Alzheimer's disease), multiple infarcts, tumors, Huntington's disease, chronic drug intoxication, AIDS, trauma, to name but a few of the many possible neurologic or other diseases which may be responsible.

Denervation atrophy. Total atrophy of skeletal muscle fibers which occurs after disconnection from their motoneurons.

Diplopia. Double vision. It can be the result of damage to the brainstem gaze mechanisms, the motor nuclei or nerves of the extraocular muscles, or disease of the muscles themselves.

Disinhibition of behavior. Patients say and do the first things that come into their heads without considering the social correctness or the future consequences of what they say or do. Can occur with bilateral damage to prefrontal lobes of the cortex or median dorsal nuclei of the thalamus.

Dizziness. Different sensory experiences described by the patient as a feeling of rotation or whirling, but also as light-headness, faintness, or swaying. Many different conditions can lead to this complaint. One subset of complaints in which the patient descibes definite feelings of rotation (whether of himself or the environment) is called vertigo , and occurs almost exclusively with disorders of the peripheral or central vestibular system. See vertigo.

Dressing apraxia. Inability to put clothes on correctly in the absence of any motor defect which would interfere with the task. The patient has lost the spatial concept of how items of clothing fit around the limbs and body. Neglect of the left side is one conspicuous component of dressing apraxia, though it is not the whole story. Seen in large lesions of the right parietal lobe (assuming a right-handed patient).

Dysarthria. Impairment of articulating words (speaking), with normal comprehension and memory of words. This is a motor disorder which involves the various muscles of the face, lips, tongue, and vocal cords that are used in speech. Dysarthria can be the result of lower motor neuron paralysis or upper motor neuron paralysis. It can also reflect incoordination of muscles due to cerebellar damage, rigidity of muscles due to damage to the extrapyramidal system, or even repetitive muscle spasms as occur in stuttering.

Dyslexia. A developmental language disorder characterized by difficulty with reading, writing and spelling. There is no loss of the ability to recognize the meaning of objects, pictures, diagrams, etc.

Dysesthesia. Abnormal sensation produced by normal stimuli. See thalamic syndrome.

Dysmetria. Improper "measuring" of distances in voluntary movements. The limb arrests too soon or overshoots the mark when the subject attempts to make a specific movement. Dysmetria is a sign of damage to pathways connecting the cerebellum with the spinal cord and brainstem, or damage to parts of the cerebellum itself.

Dysphagia. Impairment of swallowing.

Dystonia. A persistent posture or position, which seems to occur when an athetoid movement becomes "frozen" at one of its extremes. For example, the hand may remain painfully over-flexed for minutes at a time. The localization of the damage is not clear, but the extrapyramidal system is involved.

Embolus. Part of a thrombus that has broken free and traveled through the circulation until becoming lodged in a small vessel (and impeding flow). Other types of tissue, such as tumor or fat, and gas (e.g., an air bubble) can also form emboli.

Endarterectomy. Surgical removal of the lining of an artery that has become occluded or otherwise diseased.

Epicritic perceptions. These complex sensory perceptions are highly integrated, precisely localized determinations about sensory events initially detected by mechanoreceptors.The derivation of this word is from the Greek "epikrisis" meaning determination. Examples of epicritic perceptions include two-point discrimination, joint position sense, stereognosis, and graphesthesia.

Extinction (of a sensory stimulus). Recognition only on one side of bilaterally and simultaneously applied stimuli.

Fasciculations. Spontaneous contractions of all the muscle fibers in a motor unit (a fascicle of muscle fibers), which occur in early stages of muscle denervation. They presumably reflect abnormal activity of the motoneuron. Fasciculations can be seen during physical examination if the affected muscle is close to the body surface. They appear as subtle ripples or waves of contraction that pass across the skin surface.

Fibrillations. Spontaneous contractions of individual muscle fibers (cells) which occur in early stages of muscle denervation. They can be detected only by needle electrodes in the muscle, unlike fasciculations which are visible on physical exam.

Finger agnosia. The inability to name the different fingers of the two hands. Finger agnosia may be seen after left parietal lobe lesions (in right-handers). It is often accompanied by left-right confusion and an inability to do even the simplest mathematical calculations.

Finger-to-nose test. The patient is asked to alternately touch the examiner's finger and his own nose. This compound movement involves a change in posture at several joints, and if the duration and timing of muscle contractions and relaxation are abnormal, this test will demonstrate the problem. An abnormal finger to nose test indicates damage to the cerebellum and/or its connections with the brainstem and spinal cord.

Flaccid paralysis (lower motor neuron paralysis) . Paralysis with the following characteristics: 1) muscles are soft and lax. 2) muscles provide no resistance at all to passive stretching. 3) reflexes cannot be elicited (but if the paralysis is incomplete, any reflexes present will be normal e.g. Babinski response will be plantar flexion.). 4) muscles show abnormal electrical activity. Later they undergo denervation atrophy.

Foot drop. Inability to dorsiflex the foot resulting in gait difficulties, seen with paralysis of anterior muscles of the leg.

Frontal lobe abulia. Reduced motor activity of all kinds produced by bilateral damage to the prefrontal cortex , i.e. frontal lobe cortex which is located anterior to the usual primary and supplementary or association motor cortices.

Gag reflex. Reflex elicited by touching the posterior wall of the pharynx. Pharyngeal muscles contract symmetrically elevating the soft palate. Actual gagging may or may not occur. Afferent loop involves the glossopharyngeal nerve, the efferent loop involves the vagus nerve.

Glaucoma. A group of heterogeneous eye diseases resulting from an increase in intraocular pressure. Can lead to visual field defects and ultimately blindness.

Graphesthesia. Ability to identify a number or letter written on the hand (or other part of the body). Graphesthesia requires intact epicritic perception.

Hallervorden-Spatz disease. An inherited disease producing rigidity, dystonia, and choreoathetosis. The globus pallidus, substantia nigra, and red nucleus degenerate and become filled with intense brown pigmentation which apparently represents abnormal iron deposits. No current treatment reverses the disease, and certain individuals may ultimately become completely mute and rigidly immobile, i.e. "locked-in."

Heel-to-shin test. The patient is asked to place one heel on the opposite knee, and then run the heel down the front of the shin to the ankle. This compound movement involves a change in posture at several joints, and if the duration and timing of muscle contractions and relaxation are abnormal, this test will demonstrate the problem. An abnormal heel to shin test indicates damage to the cerebellum and/or its connections with the brainstem and spinal cord.

Hemianesthesia. Loss of sensation over one half of the body.

Hemianopsia (or hemianopia). Loss of one half of the visual field of one or both eyes, referred to as unilateral or bilateral hemianopsia. See visual field defects.

Hemiballismus. Involuntary wide-ranging, flinging movements of entire limb(s). Seen after damage to the subthalamic nucleus. The abnormal movements occur on the side opposite the damaged subthalamic nucleus.

Hemiparesis. Paralysis of the arm and leg (sometimes lower face as well) on one side of the body.

Hemorrhagic stroke. Caused by rupture of a blood vessel or aneurysm. Hypertension greatly increases the risk of hemorrhagic stroke especially in the thinner-walled vessels. An embolic stroke can also have a hemorrhagic component if the embolus blocks the vessel long enough to kill brain tissue and then breaks up, permitting re-perfusion of the now dead tissue.

Heteronymous. Pertaining to non-corresponding visual fields. See visual field defects.

Heteronymous hemianopsia. A loss of one half of the visual field comprised of non-corresponding field losses from each eye. See visual field defects.

Homonymous. Pertaining to corresponding visual fields. See visual field defects.

Homonymous hemianopsia. A loss of vision in the corresponding halves of the visual fields in the two eyes.  It is produced by lesions of the visual pathway behind the optic chiasm, but not by damage to the retina or optic nerve.  See visual field defects.

Homonymous quadrantanopsia. Loss of corresponding quarters of the visual fields in both eyes. Usually caused by damage to the temporal or parietal lobe optic radiations. Damage to temporal results in superior quadrant defect whereas damage to parietal lobe optic radiations results in an inferior quadrant defect. See visual field defects

Horner's syndrome. One or more of the following findings, indicating sympathetic dysfunction: 1) uneven pupils, with more constricted pupil on side of lesion. 2) mild drooping of the eyelid (weak tarsal muscles in upper lid produce little "ptosis") on side of lesion. 3) hot, flushed, dry skin on same side of face as lesion. The lesion is always on the same side as the findings. However the lesion can interrupt the sympathetic system at different levels: reticulospinal tracts of brainstem/spinal cord; intermediolateral column at T1-2; superior cervical ganglion; postganglionic sympathetic fibers, etc.

Huntington's disease. An autosomal dominant inherited disorder, usually beginning in middle age, featuring insidious progression of mental abnormalities associated with frontal lobe damage (emotional, personality, and intellectual) and motor abnormalities associated with basal ganglion damage (hence the alternate name, Huntington's chorea). Although there are exceptions, most patients with this disorder deteriorate to a vegetative state in 10-15 years. Pathological examination of the brain reveals extensive degeneration of the striatum, and to a lesser extent, frontal cortex. Molecular biology reveals abnormal expansion of the triplet repeat at the 3' end for the coding region of a newly characterized gene; its function is not yet understood.

Hyperlipidemia. Abnormally high levels of fat in the blood, increasing the risk of vascular disease.

Hypotonia. Decrease in resistance that a muscle normally offers to: 1) palpation (muscle feels soft and lax) 2) passive manipulation like flexion or extension of a limb. If accompanied by paralysis, hypotonia is a sign of lower motor neuron damage. Hypotonia also occurs in cases of cerebellar damage where both upper and lower motor neurons are intact.

Infarct. An area of dead tissue which is the result of acute ischemia.

Intention tremor. In disease of the cerebellum or its connections, the velocity and force of movements are not properly controlled. If a limb overshoots or undershoots its target, then the error is corrected with a series of jerky secondary movements in which the finger (or toe) moves side-to side before it finally reaches the target. These little movements have been called intention tremor. (In addition, patients with cerebellar damage or damage to the superior cerebellar peduncle may show a much wider-range, flapping tremor whenever they try to activate limb muscles.)

Internuclear ophthalmoplegia. Impairment of the ability to adduct one eye, without damage to the IIIrd nerve or nucleus since that eye can still move toward the midline in convergence. Internuclear ophthalmoplegia (abbreviated INO by neurologists) is produced by an ipsilateral lesion in the medial longitudinal fasciculus that damages fibers projecting to the oculomotor nucleus from the contralateral abducens nucleus.

Ischemia. Loss of blood flow.

Ischemic stroke. Often caused by a thrombus or embolus which results in blood supply being blocked. Compare to hemorrhagic stroke.

Jaw jerk. Monosynaptic reflex elicited by tapping the chin with the jaw muscles relaxed. If the reflex is hypereactive (suggesting upper motor neuron problems), contraction of the masseters can be seen or felt.

Jendrassik maneuver. Aprocedure to emphasize stretch reflexes. Patient links fingers of the hands together and makes a slight outward pull. Reflexes may also be emphasized by having the patient grit the teeth.

Joint position sense. The ability to distinguish which direction a joint is being moved, without visual cues. This is an epicritic perception.

Korsakoff's "psychosis". A defect in forming new, long-term memories in an alert and responsive individual whose other cognitive impairments are far less severe. See also Wernicke-Korsakoff disease.

Lacunar Infarct. A small cavity or lacune, produced by occlusion of a small penetrating arterial branch and the subsequent death of a small amount of brain tissue.  Lacunar infarcts most commonly occur in the basal ganglia, thalamus, base of the pons, internal capsule, and deep white matter of the hemisphere.

Lacunar Stroke. A subtype of ischemic stroke in which the affected area resembles a lacuna or cavity.

Lateral medullary syndrome. See Wallenberg's syndrome.

Left-right confusion. Loss of the concepts of "leftness" and "rightness" due to left parietal lobe damage. Compare to left-sided neglect.

Left-sided neglect (unilateral neglect). Patients ignore their left sides and the left external space. Patient is unaware of this deficit which is caused by damage to the right parietal lobe. Homonymous hemianopsia and varying degrees of hemiparesis may also be present. Compare to left-right confusion.

Lesion. Region of damage.

Lobar hemorrhage. A subtype of hemorrhagic stroke in which the ruptured vessel infarcts a region within the cerebral hemispheres (rather than, for instance, the cerebellum).

Local reflex. Reflexes involving neurons in a local region of the CNS; for example, a local reflex in the spinal cord involves just one segment.

"Locked-in" state (also called pseudocoma). Can occur from a lesion of both cerebral peduncles or from an occlusion of the basilar artery resulting in infarction of the basis pontis but sparing of the tegmentum. Patient is quadriplegic but may be able to communicate using eye-blinking. Can also occur as the final stages of Parkinson's disease, Huntington's disease and other disease of the basal ganglia. Compare to coma.

Lower motor neuron paralysis. See flaccid paralysis.

Macular sparing. Visual field deficit produced by cortical lesions in which central (macular) vision is relatively unaffected compared to peripheral vision.

Magnus-Dekleijn reflex. A rarely-observed reflex consisting of rhythmic alternating flexion and extension of the limbs, in a pattern such that flexion of the L arm and R leg and extension of the R arm and R leg alternates smoothly with extension of the L arm and L leg and flexion of the R arm and L leg in a pattern reminiscent of four-legged locomotion. This reflex is "released" in situations where the cerebral cortex is functioning abnormally. It is thought that decorticate posturing may represent a "frozen" vestige of this reflex.

Medulloblastoma. A rapidly growing embryonic tumor that arises in the posterior part of the midline cerebellum. Currently it is believed to originate from cerebellar stem cells of the external granular layer which continue to divide in the perinatal period.

Microcephaly. Literally, small head. Results from global failure of cortical migration during gestation. People with microcephaly have extremely low intelligence and no propositional language.

Monosynaptic reflex. Reflex involving only an afferent neuron and an efferent neuron, and therefore only one synapse. See stretch reflexes.

MRC scale (MRC = Medical Research Council). Standard scale from 0 to 5 used to assess muscle strength with 0 being no movement and 5 being full strength.

Multisegmental reflex. Spinal cord reflexes which involve multiple adjacent segments. The limb withdrawal reflex is a multisegmental reflex since motoneurons in several segments must be activated to withdraw an entire limb from a potentially damaging (noxious) stimulus.

Neologism. Spontaneous speech which utilizes words that are totally made up. See Wernicke's aphasia.

Neuropathy. A lesion of peripheral nervous system.

Nystagmus. Involuntary rhythmic movements of the eyes. Most commonly, movements consist of a slow movement of both eyes in one direction, followed by a fast corrective movement (a jerk) in the opposite direction. Nystagmus can be either a sign of disease in eye movement pathways (in brainstem or cerebellum) or a normal physiological response to certain stimuli. See caloric nystagmus, optokinetic nystagmus and postrotational nystagmus.

Optokinetic nystagmus. Nystagmus elicited by presenting the subject with a monotonous series of stimuli steadily moving in the same direction at the same speed. It is a normal physiological response.

Oscillopsia. A condition in which stationary objects appear to jerk back and forth or wiggle, because of involuntary eye movements. Oscillopsia can be the result of labyrinthine, brainstem or cerebellar disease; occasionally it can also involve just one eye and be the result of spontaneous contractions of motor units in an eye muscle.

Palsy. Synonym for paralysis. See also Bell's palsy, cerebral palsy.

Paralysis. The loss of voluntary movement. A lesser degree of paralysis is technically paresis. However, in everyday usage paralysis is used to mean either partial or complete loss of voluntary movement mild degree of paralysis is often described by both physicians and patients as weakness.

Paraphasic errors. Spontaneous speech that utilizes words incorrectly. See Wernicke's aphasia.

Paraplegia. Weakness or paralysis of both legs.

Paresis. Technically, a mild or incomplete paralysis. However it is commonly used interchangeably with paralysis.

Paresthesia. A prickling, tingling, or burning sensation associated with central and peripheral nerve lesions.

Parinaud's Syndrome. Paralysis of conjugate upward gaze from a lesion at the level of the pretectal area.

Parkinson's disease. A syndrome of expressionless face, poverty and slowness of voluntary movement, "resting" tremor, stooped posture, rigidity, soft voice, and an abnormal gait consisting of small, shuffling steps with difficulty in retaining balance, especially when changing directions. The disease is produced by the degeneration of dopamine neurons in the substantia nigra; its cause is unknown.

PET scan (positron emission tomography). Imaging technique which measures the cerebral concentration of positron-emitting isotopes which are incorporated into biologically active compounds. The concentration of the tracers is determined by detectors positioned outside the head, and tomographic images are constructed by a computer in a way similar to CT or MRI. PET scanning can be used to measure cerebral blood flow, oxygen uptake, or glucose utilization. The technology is available at a few large medical centers where it is used in both research and specialized clinical applications; however it is not utilized routinely in diagnosis.

Pill-rolling tremor. One form of tremor seen in Parkinson's disease. Fingers flex and extend and thumb adducts and abducts as if rolling a small object between them. Typically the tremor is diminished by voluntary movements..

Pituitary tumor. Due to the proximity of the pituitary gland to the optic chiasm, pituitary tumors can result in visual disturbances including heteronymous anopsias.

Plantar reflex. A primitive reflex elicited by mildly noxious mechanical stimulation of the sole of the foot.  The normal adult responds with curling of the toes (plantar flexion).  An individual whose corticospinal tract is not functioning correctly responds with extension of the great toe and fanning of the other toes (dorsiflexion).  This abnormal response is also called the Babinski sign.  It is seen in the normal infant under a year of age whose corticospinal tracts are not yet myelinated and in an adult whose corticospinal tracts have been injured in some way.

Plegia. Synonym for paralysis.

Positive supporting reflex.See decerebrate rigidity.

Posterior circulation. Vertebral, basilar, and posterior cerebral arteries and their branches.

Postrotational nystagmus. Nystagmus elicited by rotating the subject for several minutes, and then abruptly stopping the rotation. This is a normal physiological response.

Prefrontal leukotomy (also prefrontal lobotomy). The operation of cutting the central white matter of the prefrontal cortex (usually bilaterally) historically performed to relieve severe psychoses.

Primitive reflexes. Reflexes seen during development that are extinguished further along the developmental process. See tonic neck reflex, Babinski reflex.

Protopathic. Sensory perceptions which have immediate value to the organism by warning of potential harm -- they provide information about pain and temperature.

Ptosis. Upper eyelid drooping. Can be caused by neuromuscular weakness, cranial nerve III disorders and Horner's syndrome.

Pupillary light reflex. This is tested by having the patient gaze at a distance point in a darkened room, and then illuminating one eye. The reflex response is normally prompt constriction of both that pupil (direct response) and the other pupil (consensual response). The afferent limb of this reflex is the optic tract, which sends a few axons directly to the pretectal area. The efferent limb of the reflex involves parasympathetic components in the IIIrd nerve.

Quadrantanopsia. Loss of one-quarter of the visual field. See visual field defects

Quadriplegia. Weakness or paralysis of all four extremities.

Receptive aphasia. (also Wernicke's aphasia). A languge deficit characterized by an impairment in the comprehension of speech and relatively fluent speech which lacks meaning. Synonyms: receptive, fluent, posterior aphasia. Contrast with Broca's aphasia.

Red nucleus walking. Spontaneous standing and walking mediated at the level of the red nucleus. Pure red nucleus walking is seen only in animals surgically deprived of cerebral cortex and basal ganglia. However, the crawling behavior of infants, the Magnus-Dekleijn reflex and decorticate posturing, are all related to red nucleus walking in experimental animals.

Reflex. An involuntary motor response to a sensory stimulus.

Retrograde amnesia. Loss of memory of events prior to onset of anmesia. A component of Korsakoff's "psychosis" but also seen after transient disturbances of brain function with little or no permanent damage. Compare to anterograde amnesia.

Rinné test. A test to discriminate among possible causes of hearing impairment. A vibrating tuning fork is placed at the external auditory canal and then in contact with the mastoid process. Disease of the middle ear is suspected if the fork appears louder via bone conduction (on the mastoid) than air conduction (at the auditory canal). See also Weber's test.

Romberg maneuver. Patient stands with feet together and eyes closed. This maneuver tests the integrity of the proprioceptive system necessary for balance.

Scanning speech. A pattern of speech in which words are broken up into syllables (the term scanning is a reference to the way a line of poetry sounds when it is scanned for meter). In addition to its scanning quality, speech is slow and syllables may be uttered with either more or less force than in normal speech. This disorder indicates damage to the cerebellum.

"Scissors gait". Upon attempting to walk legs are still and adduction of thigh may be stronger than other movements so legs involuntarily cross.

Scotoma. An area of deficiency in the visual field surrounded by normal areas. A scotoma is seen in normal vision at the point of the optic disk.

Spasmodic Torticollis. A dystonia limited to certain head and neck muscles. It involves intermittent spasms of contraction of face, jaw, and neck muscles, which can be both painful and embarrassing to the affected individual. The cause is unknown.

Spastic paralysis (upper motor neuron paralysis) . Paralysis with the following characteristics: 1) distal muscles more affected than proximal muscles. 2) muscles respond abnormally to passive stretching. 3) muscle stretch reflexes are exaggerated. 4) abnormal reflexes (like an abnormal Babinski reflex) are present.

Spina bifida. Congenital condition produced by failure of fusion of the laminae of the lumbar vertebrae or of the sacrum. It occurs as a secondary consequence of failure of the posterior part of the developing neural tube to close correctly. It may be relatively mild (spinal cord remains in the vertebral canal) or severe (spinal cord or cauda equina is extruded into a meningeal cyst). In mild cases there may be no neurologic deficit unless other regions of the developing nervous system have been affected. In the severe cases where a meningomyelocele is present, there may be perineal sphincter failure and varying degrees of impaired leg function depending on the level; there also may be additional neurologic problems reflecting developmental abnormalities in the brainstem.

Stenosis. Narrowing of a vessel, duct, or other opening.

Stereognosis. The ability to describe or identify an unknown 3-dimensional object simply by mechanically manipulating it. This is an epicritic perception.

Stretch reflexes (deep tendon reflexes, myotactic reflexes). These muscle reflexes normally help maintain tone, and set the background tension of postural muscles which is needed for the performance of voluntary movements. To test these reflexes, the tendon of a muscle is tapped, causing the muscle to stretch. Sensory endings of large mechanoreceptor ganglion cell axons in the muscle spindles are stimulated. Central processes of these ganglion cells synapse directly on the motoneurons of the muscle being stretched. These excitatory synapses excite the motoneurons, leading to contraction of that muscle. Stretch reflexes are also referred to as monosynaptic reflexes or deep tendon reflexes.

Stroke. A sudden, focal, nonconvulsive neurologic deficit which is produced by a vascular event. Strokes are characterized by the abrupt onset of the deficit (a few seconds to a few days depending on the mechanism). They can be produced by either vascular occlusion (ischemia) or by hemorrhage. The specific neurologic deficits reflect both the location and the size of the lesion.

Syringomyelia. Progressive syndrome which involves the expansion of the central canal of the spinal cord and the corresponding damage to surrounding tissue.

Tabes dorsalis. One manifestation of advanced syphilis of the nervous system. It is due to degeneration of target cells in the dorsal root ganglia and all their processes including the posterior columns of the spinal cord.

Tachistoscope. Device used to display images for a brief, fixed amount of time.

Tandem gait (heel-to-toe walking). Similar to field testing for inebriation but is used to assess coordination.

Thalamic aphasia. A language problem that is seen with destruction of the pulvinar nucleus of the thalamus.

Thalamic syndrome. Produced by damage to the somatosensory nuclei of the thalamus usually due to a vascular lesion. As sensation returns, spontaneous pain may appear on the affected side of the body such that any cutaneous stimulus may have a severely painful quality.

Thrombus. A solid mass made of various combinations of platelets, fibrin, clotting factors and the cellular elements of blood that forms within the heart or blood vessels.  Thrombus often forms on the injured wall of a vessel, but loose thrombi can also form in the left atrium of the heart if it is not contracting normally so that blood stagnates there.  A thrombus may break free and become an embolus.

TIA.Transient Ischemic Attack.

Tic. (Synonym: habit spasm). Habitual movements which may range from sniffing to throat clearing to grimacing, etc. which are incessantly repeated in situations in which they are not called for (or even appropriate). The affected individual may or may not be aware of them -- and may or may not be able to consciously control them.

Titubation. Constant nodding tremor of the head. Often a sign of a medial cerebellar disorder.

Tonic neck reflex. Reflex induced when head is turned passively to one side. Results in extension of arm and leg on the ipsilateral side to the head turn and flexion of the contralateral limbs. Seen in most normal infants. In adults it can be a sign of pyramidal or extrapyramidal tract abnormality. This reflex is mediated at the level of the medulla.

"Top of the Mark" syndromes (also called "top of the basilar" syndrome). Syndromes produced by occlusion of branches at the bifurcation of the basilar artery. Clinical findings may include bilateral motor and sensory signs, cranial nerve III findings, visual problems, cerebellar ataxia and coma.

Tourette's syndrome. A rare syndrome of multiple tics, which may include snorting, involuntary grunting or high-pitched vocalization, swearing, or repetitive motor behavior like jumping up and down or turning in a circle. Afflicted individuals often report a mysterious compulsion to carry out these motor activities. So-called Touretters can be highly intelligent, creative individuals. Oliver Sacks' account of a successful surgeon who has Tourette's syndrome in An Anthropologist on Mars is fascinating. A number of drugs currently on the market can reduce the symptoms in these individuals. However many report that these drugs also blunt their energetic and creative personalities, and they prefer to live with the "compulsions" of their disease. Tourette's syndrome apparently involves metabolic alterations centered in the caudate nucleus, although other parts of the extrapyramidal system may also be involved.

Transient ischemic attack. (Commonly abbreviated TIA) A brief, self-reversing episode of focal, nonconvulsive neurologic disturbance produced by temporary ischemia. There are no lasting neurologic deficits once the attack has ended. However, TIAs provide a warning of an imminent stroke; more than 25% of individuals who have a TIA will have a stroke (often producing permanent neurologic deficits) within 5 years.

Trigeminal neuralgia. Attacks of extreme pain in a distribution of one or more divisions of the trigeminal nerve.

Two-point discrimination. The ability to distinguish whether the skin is being touched by 2 objects very close together or by a single object, without visual cues. This is an example of a complex epicritic perception.

Upper motor neuron paralysis. See spastic paralysis.

Vertigo. A feeling that objects in the environment are spinning around or moving, or the sensation that the head is whirling, or sometimes the feeling that the floor and walls seem to sink and rise, or that the body is leaning. Often the feelings are accompanied by nausea, vomiting, and difficulty walking, and can be relieved by sitting or lying still. Usually vertigo indicates disease of the vestibular end-organ, the vestibular division of the VIIIth nerve, vestibular brainstem nuclei, or vestibular parts of the cerebellum. See dizziness.

Vestibulo-ocular reflex. Reflex which stabilizes the optical axis during motor activity, by producing counteracting movements of the eyes, head, or body.

Vibration sense. The ability to detect vibrating objects through touch. A tuning fork is used to assess this sense which is carried by large heavily myelinated axons in the dorsolateral funiculus.

Visual Field Defects. A heterogenous group of visual problems that can result in blind areas of the visual field. Visual field defects can result from damage anywhere along the visual pathway including lesions at the retina, optic nerve, optic chiasm, optic tract, lateral geniculate nucleus, optic radiations and at the visual cortex. Examples of visual field defects include: homonymous hemianopsia, heteronymous hemianopsia (such as binasal hemianopsia, bitemporal hemianopsia), homonymous quadrantanopsia.

Wallenberg's syndrome (Lateral medullary syndrome). A group of signs/symptoms produced by damage to the dorsolateral regions of the medulla. Deficits may include some or all of the following: 1) Loss of pain and temperature sensation: ipsilateral on face, contralateral on body. 2) Hoarseness, impaired swallowing, diminished gag reflex. 3) Ataxia of ipsilateral arm and leg, falling or veering to the side to the lesion. 4) Decreased muscle tone in ipsilateral arm and leg (no paralysis). 5) Nystagmus, diplopia. 6) Vertigo. 7) Horner's syndrome. This is the commonest brainstem stroke.

Wallerian degeneration. Loss of axons and any surrounding myelin distal to the point where an injury has disconnected axons from their nerve cell bodies of origin.

Weakness. Mild degreee of paralysis.

Weber's Test. A test to detect whether a hearing loss is sensory (i.e. inner ear and eighth nerve) or conductive (i.e. middle ear) in origin. A vibrating tuning fork is placed midline on the forehead. In a normal person the sound is heard equal in each ear. If the patient has a conductive hearing loss than the sound is heard best in the ear with the loss. If the patient has a sensory hearing loss then the sound is heard best in the unaffected ear.

Wernicke-Korsakoff disease. A disease produced by thiamine deficiency (most often in patients with long-standing chronic alcoholism). Symptoms include ocular abnormalities (nystagmus, conjugate gaze paralysis), ataxia, and global confusion, all of which may be corrected by giving thiamine. However there will then be an enduring defect in learning and memory (this is the Korsakoff component). Compare with Korsakoff's "psychosis".

Wernicke's aphasia. (Synonyms: posterior or fluent aphasia) A primary deficit in the comprehension of speech, accompanied by relatively fluent speech which is properly intoned and articulated, but is largely nonsensical. The patient is unaware of the problem. He or she cannot understand what is said, or read with comprehension. In right-handers, the lesion usually lies in the planum temporale of the left temporal lobe or in adjacent regions.

Withdrawal reflex. The involuntary pulling back of a limb from a noxious stimulus. This is an example of a multisegmental spinal reflex. It is often accompanied by crossed extension of the opposite limb, which enables the organism to stay upright.