The Neuroscience on the Web Series:
Glossary of Neuroscience Terms A-B

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z


difficulties with arithmetic; may be the result of damage to the angular gyrus in the hemisphere dominant for speech and language
acceleration-deceleration trauma:
According to Love and Webb (1992) the most predominant injury type is acceleration-deceleration trauma. Acceleration-deceleration trauma causes discrete lesions which affect only certain areas of the brain, occurs when the head is accelerated and then stopped suddenly, as in a car accident, and causes discrete, focal lesions to two areas of the brain, The prefrontal areas and the anterior portion of the temporal lobes. The brain will suffer contusions at the point of direct impact and at the site directly opposite the point of impact due to the oscillation of the brain within the skull.

It should be noted that brain injuries may occur as a result of acceleration-deceleration trauma
unaccompanied by impact.
a neurotransmitter for motor neurons that is involved in the inhibitory function (as is dopamine) of the basal ganglia
afferent fibers:
nerve fibers that take messages from the periphery to the brain; afferent fibers are almost always sensory fibers
acquired disturbance of reading due to brain injury (Love and Webb, 1996, p. 314)
lack of sensory recognition as the result of a lesion in the sensory association areas or association pathways of the brain. An example is looking at a common object but not recognizing it, or associating meaning with the image.
acquired disturbance of writing due to brain injury (Love and Webb, 1996, p. 314)
alexia with agraphia:
difficulties with reading and writing; may be the result of damage to the angular gyrus in the hemisphere dominant for speech and language
alpha cells:
the principle lower motor neurons of the spinal cord (they are located on the ventral aspect of the cord); they form the main part of the final common pathway and conduct rapid motor impulses; each alpha cell innervates approximately 200 muscle fibers
alternating hemiplegia:
paralysis of different structures on each side of the body; this condition may be the result of a lesion in the brain stem that damages both the nucleus of a cranial nerve and one side of the upper motor neurons of the pyramidal tract
a structure which is attached to the tail of the caudate nucleus; it is considered to be a part of the limbic system and is involved in emotion
communication or connection between the separate components of a branching system; as in the Circle of Willis, anastomosis allows blood carried by different arterial branches to come together and be redistributed
angular gyrus:
the gyrus that lies near the superior edge of the temporal lobe, and immediately posterior to the supramarginal gyrus; it is involved in the recognition of visual symbols (Geschwind referred to it as the "association cortex for association cortices" and "the most important cortical areas of speech and language"). Lesions in this area can result in alexia and agraphia.
difficulty with word-finding or naming; anomia may be the result of damage to the angular gyrus in the hemisphere dominant for speech and language. According to Goodglass and Kaplan (1983), anomia can be localized with the least reliability of any of the aphasic syndromes. Also, according to Keenan (1975) all patients with Aphasia experience some problems with word finding.
a loss of the sense of smell; may be a result of a lesion on the olfactory pathway
toward the front (opposed to posterior)
anterior cerebral artery:
a branch of the internal carotid artery; the anterior cerebral artery supplies blood to the medial cortex, some areas of the frontal lobe, and the corpus striatum
anterior commissure:
one of the three major groups of commissural fibers; part of the Circle of Willis, the anterior commissure connects the temporal lobes, as well as connecting the temporal lobe to the amygdala and to the opposite occipital lobe; it is also connected to the corpus callosum
anterior communicating artery:
an artery which arises from the internal carotids; it joins together the anterior cerebral arteries of each hemisphere
the main artery supplying blood to the body (with the exception of the lungs); it ascends from the heart then forms an arch, from which two subclavian arteries arise
a disturbance of the skills, associations, and habits of language due to injury to certain brain areas that are specialized for these functions. Disturbances of language usage that are due to paralysis or incoordination of the musculature of speech or writing or poor vision or hearing are not, of themselves, aphasic." Thus, aphasia can affect auditory comprehension, oral expression, reading and writing. (Goodglass and Kaplan, 1983)
comes from the Greek word "praxis," which means action. According to Halperin (1986 in Chapey, 1986, p.422), "apraxia of speech is an articulation disorder that results from impairment due to brain damage, of the capacity to order the positioning of speech musculature and the sequencing of muscle movements for volitional production of phonemes and sequences of phonemes; but it is not accompanied by significant weakness, slowness, or incoordination of these same muscles in reflex and automatic acts."
Apraxia of speech is a disruption of the capacity to program the skilled oral movements necessary for speech. The problem is with the programming associated with incorrect neural commands at higher, more central levels. In the past, apraxia was often classified as a type of articulation disorder and was in fact called central dysarthria by some. Now, it is considered a motor planning/programming deficit. According to Wertz (1984), apraxia of speech "is a neurogenic phonological disorder, resulting from the sensorimotor impairment of the capacity to select, program and execute coordinated movements of the speech musculature for the production of voluntary speech." In other words, the part of the brain that generates the motor programs for speech/phonology is damaged. Kearns and Simmons (1989, in Northern, 1989) reported that research using spectographic analysis of voice onset time (VOT) supports the programming position. Includes limb apraxia, oral apraxia, apraxia of gait, and apraxia of the swallow.
apraxia of gait:
difficulty with programming the motor movements involved in walking
apraxia of the swallow :
inability to swallow volitionally.
apical dendrites:
a type of dendrite which has a stalk that is filled with cytoplasm, these appear to be part of the soma of the neuron to which they are attached; the majority of apical dendrites are found in the cerebral cortex
Aqueduct of Sylvius (cerebral aqueduct):
a channel which connects the third and fourth ventricles
arachnoid mater:
the middle layer of the meninges; in some areas it has projections (arachnoid granulations or villi) into the sinuses formed by the dura mater
arachnoid villi (arachnoid granulations):
projections of the arachnoid mater into the sinuses formed by the dura mater that transfer cerebrospinal fluid back into the bloodstream
arcuate fasciculus:
the groups of fibers that connect Broca's area with Wernicke's area (these fibers connect to the angular gyrus) and are located below the supramarginal gyrus. According to Geschwind, damage to this area results in Conduction Aphasia.
formation of "plaque" consisting of muscle cells and fats on arterial walls making the flow of blood through  arteries more difficult. Informally, "hardening of the arteries"
arteries of stroke:
striata arteries, which are branches of the middle cerebral arteries
ascending reticular formation (reticular activating system):
the component of the reticular formation that is responsible for the sleep-wake cycle; it mediates various levels of alertness
occurs whenever food enters the airway below the true vocal folds. Aspiration can occur before, during, or after the swallow.
association fibers:
nerve fibers that connect areas within the same lobe or between lobes, within the same hemisphere; the most prevalent type of neuroal tracts found in the cortex
an incoordination of motor movement; ataxia results from cerebellar lesions; the term may also be used to describe the unsteady walk and unusual postures seen in patients who have suffered injury to the cerebellum
ataxic dysarthria (cerebellar dysarthria):
a disorder that results in jerky, uncoordinated movements of the speech musculature; it is caused by lesions in the cerebellum
disorder that causes slow writhing movements of the entire body but especially of the arms, face and tongue.
auditory association areas:
Brodmann's areas 21 and 22
auditory comprehension:
the ability to understand spoken language
autonomic nervous system:
one of the three main divisions of the nervous system; it innervates the involuntary structures of the body (e.g., heart, smooth muscles, glands) and is involved in control of automatic and glandular functions; it is divided into two parts, the sympathetic and parasypathetic
the part of the neuron that allows it to send messages to other nerve cells; although each neuron can have only one axon, the axon itself can have many branches which connects it to many others  


contrast material, not radioactive, used during barium and modified barium studies
basal ganglia:
the largest subcortical structure of the brain; it is made up of the caudate nucleus and the lenticular nucleus; it is located at the level of the thalamus
basilar artery (vertebral basilar artery):
the artery that is formed when the two vertebral arteries join together at the lower border of the pons; the basilar artery again divides at the superior border of the pons to form the posterior cerebral arteries (other arteries that arise from the basilar prior to this division include the anterior cerebellar arteries, inferior cerebellar arteries, posterior cerebellar arteries, and the pontine branches)
basilar dendrites:
a type of dendrite that does not have a stalk; these are more numerous than apical dendrites
BDAE: Boston Diagnostic Aphasia Examination
developed by Goodglass and Kaplan in 1972, is currently being revised. (I was asked by the publishing company to critique/review the upcoming edition. It promises to be quite good.) At the moment it consists of twenty-seven subtests divided into the following sections: conversational and expository speech, auditory comprehension, oral expression, understanding written language, and writing. The severity of a patient's aphasia can be rated on a scale from one to seven based on speech and language characteristics as well as auditory comprehension. The Boston Naming Test, a test for anomia which was developed to be used along with the BDAE, is the supplementary instrument most often used in the evaluation of aphasia (Chapey, 1994).
bilateral innervation:
both left and right nuclei of a pair of cranial nerves receive innervation from both the left and the right motor pyramidal tracts, provides both ipsilateral and contralateral innervation
biological intelligence:
the complex cognitive processes (such as reasoning and judgment) that are mediated by the most anterior part of the frontal lobe
BDAE: Boston Diagnostic Aphasia Examination
slowed heart rate
the "reduced speed of movement of a muscle through its range" (Love & Webb, 1992, p. 146).
brain stem:
the midbrain, pons, and medulla oblongata
slow heart rate
broad-based gait:
a term used to describe the way in which some patients compensate for problems related to cerebellar injury by walking with their feet far apart
Broca's aphasia:
affects the third frontal convolution (both the gyrus and the sulcus) of the left frontal lobe. ( Broca's area, Brodmann's area #44)
Characteristics are telegraphic speech, affected syntax, as well as labored and slow speech, Melodic Contour is flat and Articulatory Agility is impaired. Potential problems include: simplification of consonant clusters (e.g. t/st, p/spl) and distortion of phonemes, substitutions are infrequent. A few paraphasias may occur. They will usually be literal. Repetition is typically impaired, as is Word finding. Auditory Comprehension is superior to expressive language. The patient's ability to understand grammatical morphemes will be affected. So, while it can be said that auditory comprehension is good in comparison to that of Wernicke's aphasics, it is not normal.

Token Test (DeRenzi & Vignolo, 1966), which assesses subtle receptive language dysfunction, can be used to evaluate the auditory comprehension of Broca's aphasics and to help distinguish between Broca's aphasia and verbal apraxia.  Also, limb apraxia may not allow the patient to carry out the instructions, even though he/she understands them.

Hemiplegia/Hemiparesis of the right side is common in left hemisphere lesions causing Broca's aphasia (remember, the language center is in the left hemisphere for more than 90% of the population) The face and arm are most likely to be affected due to the organization of the motor strip.Apraxia frequently accompanies this type of aphasia as it is also caused by lesions to area 44. Broca's aphasics typically have low frustration tolerance. They are aware of their errors and may respond to them with a catastrophic reaction which might include crying, screaming and yelling, etc.
Broca's area:
the area of the brain involved in the programming of motor movements for the production of speech sounds; it is also involved in syntax; Broca's area is located on the inferior third frontal gyrus in the hemisphere dominant for language; injuries here may result in apraxia or Broca's aphasia
Brodmann's Classification System:
a map of the cortex developed by neurologist Korbinian Brodmann that classifies the different areas of the brain by number
buccinator muscle (oral cavity):
holds food in contact with the teeth. with the obicularis oris and zygomaticus all three are  innervated by the facial nerve (CN. VII).
bulbar lesions:
injuries to the nuclei of the cranial nerves located in the brain stem; they are considered to be lesions of the final common pathway: usually bilateral, they produce bulbar palsy
bulbar palsy:
paralysis produced by bulbar lesions