Cerebral Cortex and Higher Functions

Question 1

Lesions in cortical areas

Answer 1

generally result in deficits that begin with the letter A, including apraxia, agnosia, aphasia, amnesia, alexia, acalculia, abulia, and anopsia

Question 2

Lesions limited to M1

Answer 2

rare

these patients may have a contralateral weakness most evident in distal muscles that may or may not be accompanied by hyperreflexia and a Babinski sign.

Question 3

Damage to premotor cortex and supplementary motor cortex

Answer 3

may result in an apraxia, a disruption of the patterning and execution of learned motor movements. Individual movements are intact and there is no weakness, but the patient is unable to perform learned movement in the correct sequence.

Commonly, lateral frontal lobe lesions affect both primary motor and premotor cortical areas and result in weakness combined with apraxia.

Question 4

Lesions in the prefrontal area

Answer 4

result in frontal lobe syndrome. Patients may exhibit changes in behavior, intelligence, cognitive or executive functions, and memory.

behavior changes include a lack of appreciation and disregard for social rules, emotional withdrawal, a decrease in motivation, and abulia. Patients with abulia have a condition in which they lack sufficient levels of awareness to initiate a change in behavior

patients may test normally for intelligence but perform in an unintelligent manner.

A decrease in cognitive abilities includes an inability to modify behavior in response to changing stimuli, impaired problem solving, and an inability to organize or plan. Patients may exhibit perseveration, an abnormal repetition of specific behaviors.

Question 5

prefrontal cortex lesions

Answer 5

patients with prefrontal cortex lesions may have short term or working memory loss

premotor lesions may also result in the emergence of infantile suckling or grasp reflexes that are suppressed in adults. IN the suckling reflex touching the cheek causes the head to turn toward the side of the stimulus as the mouth searches for a nipple to suckle.

In the grasp reflex touching the palm of the hand results in a reflex closing of the fingers which allows an intact to grasp anything that touches the hand.

Question 6

Changes in the activity of neurons in the frontal lobe

Answer 6

may be the causes of unipolar or bipolar disorders, the two most common mood disorders

unipolar depression is the most common mood disorder and may result from decreased neuronal activity in the frontal lobes inferior to the genu of the corpus callosum

patients with bipolar disorder experience recurrent episodes of depression and euphoria or mania. In periods of euphoria there is increased activity in the frontal lobes inferior to the genu of the corpus callosum

Question 7

Lesions in the lateral aspect of the left hemisphere

Answer 7

aphasias are disorders of language that result mainly from lesions in the lateral aspect of the left hemisphere. Aphasias may be caused by a stroke involving superficial branches of the left middle cerebral artery (MCA). Patients with an aphasia commonly have agraphia and difficulty in repetition or naming.

Question 8

Damage to Broca’s Area

Answer 8

damage to this area produces a motor, confluent, or expressive aphasia which results in difficulty in putting together words to produce expressive speech

patients with expressive aphasia can understand written and spoken language but their verbal output is usually reduced to single syllable words. They also have agraphia, although the hand used from writing can be used normally in other tasks. They are aware of and frustrated by their aphasia and have difficulty in repetition because of their lack of the ability to express their thoughts verbally or in writing

Question 9

Lesion of Broca’s area

Answer 9

may include the adjacent primary motor cortex and result in a lesion of corticobulbar neurons arising from the left hemisphere and weakness of the muscles of the lower face on the right.

If the lesion is large, there may be a spastic hemiparesis of the right upper limb.

If the left frontal eye field is involved the patient will look to the left, away from a paralyzed right upper limb.

Question 10

Lesions in Broca’s area in the right hemisphere

Answer 10

lesions in the area equivalent to Broca’s (and Wernicke’s) in the right hemisphere are commonly caused by a stroke involving superficial branches of the right middle artery and result in dysprosody. These patients have normal speech and comprehension of speech but cannot express or do not comprehend the emotional and tonal qualities of speech that are crucial to verbal communication

Question 11

Lesions in the somatosensory cortex

Answer 11

result in impairment in the perception of somatic sensations on the opposed side of the face, scalp, trunk, and limbs

the primary somatosensory cortex may reorganize after injury to peripheral receptors or to the primary sensory neurons that innervate them. For example, the loss of sensory input from an amputated digit 3 results in the cortical area responsive to that digit reorganizing so that its neurons now respond to the adjacent digits 2 and 4.

Question 12

lesions of the superior parietal lobe

Answer 12

including areas 5 and 8, usually in the dominant hemisphere may result in one of several forms of apraxia or a stereognosis

these patients may have an ideational apraxia, a lack of understanding of how to organize the sequence of a pattern of movements

they may have an ideomotor apraxia, in which they cannot perform tasks on command, even though there is no motor weakness. They may be able to identify an object correctly but will not know how to use it.

They may have a constructional apraxia, in which they are unable to copy a simple diagram or describe how to get from their home to the store

they may have astereognosia an inability to recognize an object held by its size and shape without looking at the object

Question 13

Lesions in Wernicke’s Area

Answer 13

Area 22 of the temporal lobe result in a fluent, receptive, sensory, or Wernicke’s Aphasia

Question 14

Lesion to the angular gyrus

Answer 14

area 39

in the left inferior parietal lobule may result in a loss of ability to comprehend written language (alexia) and to write it (agraphia) but spoken language may be understood.

Question 15

Lesion to the inferior parietal lobule

Answer 15

patients with a lesion may have Gerstmann;s syndrome. These patients have acalculia (inability to perform simple arithmetic problems) finger agnosia (inability to recognize fingers), and right left disorientation. Alexia with agraphia may also be present

Question 16

Lesion in areas 39 and 40

Answer 16

a lesion in the inferior parietal lobule of the right hemisphere results in contralateral neglect

these patients lack awareness of or neglect the contralateral half of the body. Although somatic sensation is intact, the patients ignore the left half of their body and may fail to dress, undress, or take care of the affected side

if these patients are asked to draw the numbers on a clock face from memory they will draw all 12 numbers on the right side ignoring the left half of the clock face. These patients deny that an arm or leg belongs to them when the affected limb is brought into their field of vision or may deny their deficit entirely

unilateral neflect is uncommon in patients with a left parietal lobe lesion because of compensation of perceptual awareness by the right hemisphere

Question 17

Cortex lesions and visual field deficits

Answer 17

a complete unilateral lesion of primary visual cortex results in a contralateral homonymous hemianopsia with macular sparing usually resulting from an infarct of a branch of the posterior cerebral artery (PCA). The area of the macula of the retina containing the fovea is spared because of a dual blood supply from the PCA and MCA. Bilateral visual cortex lesions result in cortical blindness

Question 18

Injury to the back of the head

Answer 18

may result in a loss of macular representation of the visual fields

Question 19

Unilateral lesions in the lingual gyrus

Answer 19

area 37

result in hemiachromatopsia in which the patient notes a change in the appearance of colors. Bilateral lesions result in a complete loss of color vision so that the patient sees only in shades of gray

Question 20

Parietal lesions affecting motion and depth

Answer 20

may result in Balint syndrome which includes visual disorientation, ocular apraxia, and optic apraxia

patients with visual disorientation cannot appreciate more than one aspect of a visual scene at a time

patients with ocular apraxia cannot focus on an object of interest, have difficulty initiating saccades, and tend to overshoot or undershoot visual targets

patients with optic ataxia have difficulty reaching for an object under visual control but are able to touch their nose easily with a finger

Question 21

unilateral damage to the primary auditory cortex

Answer 21

may have a slight bilateral hearing loss and difficulty localizing the source of a sound

Question 22

Lesions in area 22 in the temporal lobe

Answer 22

result in a fluent, receptive, or Wernicke’s aphasia

cannot comprehend spoken language and may or may not be able to read, depending on the extent of the lesion. The deficit is characterized by fluent speech, but it lacks meaning. Patients may speak in complete sentences but frequently misuse words

they have difficulty with repetition because they do not understand the command, are generally unaware of their deficit, and are not concerned about their condition

in deaf patients who communicate by sign language a lesion to Broca’s or Wernicke’s area will result in a corresponding motor or sensory sign aphasia

Question 23

Lesions of the arcuate fasciculus

Answer 23

results in a conduction aphasia, a disconnect syndrome in the left hemisphere

verbal output is fluent but the patient misuses words

language comprehension is normal, but the patient cannot repeat words or execute verbal commands by an examiner (such as counting backward beginning at 100) and demonstrates poor object naming

the patient is aware of the deficit and frustrated by the inability to execute a verbal command that was head and understood

Question 24

Lesions in the temporal association cortex

Answer 24

lesions in the parvocellular stream to temporal association cortex result in visual agnosias

these patients acknowledge the existence of an object that they feel or see (unlike patients with neglect) but cannot identify the object using visual input

patients may develop prosopangnosia - an inability to recognize familiar people by sight. As soon as the person speaks however, he or she is recognized

Question 25

Corpus callosum lesions

Answer 25

lesions of commissural fivers in parts of the corpus callosum result in disconnect syndromes in which regions of the 2 hemispheres can no longer communicate with each other

Question 26

Lesions to the body of the corpus callosum

Answer 26

may result in a transcortical ideomotor apraxia caused by an occlusion of the ACA

As with other forms of apraxia, there is no motor weakness but the patient cannot execute a command to move the left arm. The patient understands the command which is perceived in Wernicke’s Area of the left hemisphere but the callosal lesion disconnects Wernicke’s from the right motor cortex so that the command cannot be executed.

The patient is still able to execute the command to move the right arm because Wernicke’s area in the left hemisphere is able to communicate with the left motor cortex without using the corpus callosum

Question 27

Lesion of the splenium

Answer 27

-caused by an occlusion of the left PCA may result in alexia without agraphia

Question 28

alexia without agraphia

Answer 28

a disconnect syndrome that prevents visual information in the right occipital cortex from reaching language comprehension centers in the left hemisphere

patients can see words in the left visual field but do not understand their meaning

patients are unable to read and often have a color anomia (inability to name colors)

these patients can write but they cannot read what they wrote

-a lesion of the left occipital cortex may also result in a right homonymous hemianopsia with macular sparing

Question 29

Alexia with agraphia

Answer 29

an inability to read or write, may result from a lesion of the angular gyrus in the left parietal lobe

Question 30

Internal capsule lesions

Answer 30

a lacunar stroke involving the posterior limb of the internal capsule may result in a complete contralateral anesthesia, contralateral hemiplegia, constralateral homonymous hemianopsia, and a slight bilateral hearing loss

a lacunar stroke involving the genu of the internal capsule may result in contralateral lower face weakness, transient deviation of the uvula toward the lesion, and deviation of the tongue away from the lesion on protrusion

Question 31

Lesion of either component of the ascending arousal system

Answer 31

may disrupt consciousness and may result from lesions of the midbrain, diencephalon, or cortex

lesions caudal to the pons generally do not affect consciousness

patients are in a coma if they do not make any response to a strong sensory stimulus (i.e. rubbing the skin over the sternum with a knuckle)

the EEG of a comatose patient exhibits fixed patterns that do not vary cyclically like the EEG during non-REM and REM sleep

Question 32

Lesion of the posterior hypothalamus

Answer 32

promote sleepiness

-may also be caused by antihistamines which block the activity of the histaminergic neurons in the posterior hypothalamus

Question 33

Changes in sleep patterns with aging

Answer 33

there is a decline in the length of time spent in sleep and a decrease both in time sent in non-REM and REM sleep

elderly spend little time in stage IV slow wave sleep and exhibit frequent brief awakenings after periods of REM sleep

Question 34

Insomnia

Answer 34

an inability to initiate or obtain enough sleep

may be a symptom of anxiety, depression, chronic pain, or drug abuse

EEG shows no irregularities, but these patients do not seem to benefit from a period of sleep

Question 35

Sleep apnea

Answer 35

when breathing stops for up to 30 seconds during sleep and is associated with loud snoring

obstructive sleep apnea may be caused by abnormalities that narrow the respiratory pathway such as a deviated nasal septum or enlarged nostrils

central sleep apnea results from an inhibition of brainstem respiratory centers. Polysomnograms are used to distinguish whether a patient has a central or an obstructive sleep apnea

Question 36

Narcolepsy

Answer 36

results from an intrusion of REM sleep into the awake state

patients have daytime sleep attacks, cataplexy, a sudden loss of muscle tone and control (which may cause them to fall if standing), dreamlike hallucinations, and sleep paralysis (after awakening the patient is unable to move for several minutes)

Question 37

Other sleep disorders

Answer 37

sleepwalking, sleep terrors, and nocturnal bed wetting are parasomnias that occur during non-REM stage III or stage IV sleep

Question 38

Epilepsy

Answer 38

a CNS disorder characterized by recurrent repetitive seizures

patient who has status epileptics has continuous episodes of rapidly repetitive seizures that last longer than 30 minutes

Question 39

MCA occlusion

Answer 39

an occlusion of either MCA may result in contralateral upper limb and face hemiparesis, contralateral upper limb and face hemianesthesia, contralateral homonymous hemianopsia, and deviation of the eyes toward the affected hemisphere

patients with left MCA involvement may also have a Brocas, Wernickes, conduction, or global aphasia

patients with right MCA involvement may have contralateral hemineglect or dysprosody

Question 40

Occlusion of the ACA

Answer 40

a stroke involving either ACA may result in contralateral lower limb hemiparesis, contralateral lower limb hemianesthesia, transcortical apraxia (if only one corpus callosum is involved), and frontal lobe behavioral deficits

Question 41

Occlusion of PCA

Answer 41

an occlusion of either PCA may result in contralateral homonymous hemianopsia with macular sparing

with left PCA involvement (which also supplies the splenium of the corpus callosum) patients may also have alexia without agraphia