Cortical Lesions

Question 1

what are the objectives of this lecture?

Answer 1

1) Understand the role the frontal, temporal, parietal, and occipital lobes in human cognition
2. Appreciate the three major frontal lobe syndromes

3. Recognize the major cognitive disorders related to temporal lobe lesions
4. Understand the syndrome of hemineglect as a prototype parietal lobe syndrome
5. Know the difference between visual field deficits and visual agnosia

Question 2

describe the anatomy of the cerebral cortex

Answer 2

The cerebral cortex is the outermost layer of the brain, and averages 3 mm in thickness.

• The six-layered neocortex makes up most of the cortical surface, but the hippocampus in the temporal lobe - important for memory - is comprised of phylogenetically older three-layered allocortex.
• most enduring subregion designation is brodmann areas

Question 3

what is the difference between macroconnectivity and microconnectivity?

Answer 3

Extensive connections exist between adjacent cortical neurons via abundant synapses (microconnectivity),
*and white matter connections link remote neuronal systems into functional ensembles involving ipsilateral cortices, contralateral cortices, and subcortical nuclei (macroconnectivity).

Question 4

What is the frontal lobe essential for (affiliations/actions)?

Answer 4

Voluntary movement
Language fluency (left)
Motor prosody (right)
Comportment 
Executive function 
Motivation

Question 5

What is the temporal lobe essential for (affiliations/actions)?

Answer 5

Language comprehension (left)
Sensory prosody (right)
Memory
Emotion

Question 6

What is the parietal lobe essential for (affiliations/actions)?

Answer 6

Tactile sensation
Visuospatial function (right)
Attention (right)
Reading (left)
Writing (left)
Calculation (left)

Question 7

What is the occipital lobe essential for (affiliations/actions)?

Answer 7

Vision
Visual perception
Visual recognition

Question 8

Cortical lesions can be of the diffuse or focal category. What might cause these?

Answer 8

Examples of diffuse cortical dysfunction include Alzheimer’s Disease and hypoxic injury.
*Focal disorders are usually those related to vascular disease (stroke), traumatic brain injury (contusion, hemorrhage), and neoplasia (brain tumor).

Question 9

stroke can be really detrimental to life why?

Answer 9

A large portion of this disability is due to cognitive dysfunction from aphasia, amnesia, visuospatial impairment, hemineglect, agnosia, and a host of related syndromes.

Question 10

What are the most important non-penetrating TBI locations?

Answer 10

Contusions of the cortical surface are the most important of the cortical lesions seen in non-penetrating TBI. These tend to cluster in the frontal and temporal lobes, which are adjacent to bony prominences in the anterior and middle cranial fossae.

Question 11

what area of the cortex is injured in Broca’s aphasia?

Answer 11

Broca’s aphasia, covered in the Speech and Aphasia lecture, which results from lesions in Broca’s area of the left hemisphere (Brodmann areas 45 and 45).

Question 12

Broca’s aphasia might present with what other clinical syndrome due to the cortical architecture?

Answer 12

An analogous syndrome (to Broca’s aphasia) also occurs with lesions of the same region of the right hemisphere: motor aprosody.
*The right hemisphere is specialized for mediating the prosody of speech – the emotional content – and motor aprosody refers to the inability to inflect speech with emotion.

Question 13

what are the three syndromes to keep in mind with frontal lobe lesions?

Answer 13

• disinhibition- from orbitofrontal lesions,
• executive dysfunction- from dorsolateral prefrontal lesions, and
• apathy- from medial frontal lesions.
• These syndromes are all more florid and persistent with bilateral lesions.

Question 14

Describe the syndrome of disinhibtion

Answer 14

Disinhibition is a disorder of comportment, whereby a person can no longer adequately integrate limbic drives into an appropriate behavioral repertoire.
*Irritability, loss of empathy, impulsivity, hypersexuality, hyperphagia, and even violence can be sequelae.

Question 15

Describe what a loss of executive function due to a frontal lobe lesion would look like?

Answer 15

Executive function is a critical domain that involves the capacity to plan, carry out, and monitor a sequential goal-directed action.
*A related and disabling deficit is perseveration, the failure to alter one’s actions in response to changing environmental stimuli.

Question 16

Describe the syndrome of apathy that is tied to frontal lobe lesions

Answer 16

Apathy is the loss of motivation, and more severe forms are known as abulia and akinetic mutism. In these cases, an erosion of initiative may be so dramatic that it seems the individual’s will has been diminished.

Question 17

What is the temporal lobe aphasia we should know about?

Answer 17

Wernicke’s aphasia, in which auditory comprehension is impaired because of a lesion in the posterior region of the left superior temporal gyrus (Wernicke’s area, Brodmann area 22).

Question 18

Wernicke’s area is on the left hemisphere (almost all the time) because of hemispherical dominance of language. The other hemisphere (right) as an analgous area to the wernicke’s area, however. What does a lesion to this area produce?

Answer 18

sensory aprosody, which means diminished ability to comprehend the emotional inflection of speech, and is due to a lesion in the right hemisphere analogue of Wernicke’s area.

Question 19

H.M. is responsible for the addage “surgery must be restricted to one hippocampus at all costs”. Why?

Answer 19

This man was subjected to bilateral hippocampal resections in 1954 for the relief of intractable epilepsy, and although the surgery was effective, he was left with permanent amnesia, or new learning deficit. From then on it was clear that the hippocampus is essential for new learning, and among many lessons learned, restriction of surgery to just one hippocampus is imperative.

Question 20

Emotion is tied to what lobe?

Answer 20

Temporal lobe

Question 21

The limbic system is responsible (general) for what?

Answer 21

there is general agreement that what might be called basic emotions – influencing the flight or fight reaction, feeding, and sexuality – are mediated by the limbic system, a group of interconnected structures within the temporal lobe and the diencephalon.

Question 22

where, in practice, are temporolimbic lesions affecting emotion most commonly seen?

Answer 22

temporolimbic lesions affecting emotion are most often the epileptogenic lesions seen in patients with seizure disorders (epilepsy).

Question 23

Temporal lobe epilepsy displays the importance of the temporal lobe in emotion how?

Answer 23

In the interictal state of TLE patients, considerable evidence suggests that lasting personality changes can occur that represent an alteration in emotional function; deepened emotionality, hypergraphia, and many personality alterations may develop

Question 24

The parietal lobe is most important for what?

Answer 24

the parietal lobes are prominently involved with tactile sensation, but also with visuospatial function, attention to the contralateral side of space, reading, writing, and calculations.

Question 25

what is hemineglect?

Answer 25

• important feature of parietal lobe lesion
• hemineglect, or the failure to report, respond to, or orient to sensory stimuli that cannot be explained by primary sensory dysfunction.

Question 26

A parietal lobe lesion in what hemisphere is going to cause hemineglect?

Answer 26

Because the right hemisphere is dominant for attention, inattention to one side of the body or extrapersonal space (hemineglect) is much more common and persistent after right hemisphere lesions.
*Left hemineglect is a disabling disorder of cognition that may be overlooked unless its origin and significance are understood.

Question 27

Everyone knows the occipital lobe is all about vision. What are the higher visual function areas?

Answer 27

Higher visual function also involves association areas situated anterior to the visual cortices: the occipitotemporal (“ventral stream” or “what” system) occipitoparietal (“dorsal stream” or “where” system) cortices.
*These regions are important for attaching meaning to visual input, and damage to them produces various types of recognition deficits, collectively called visual agnosia.

Question 28

Higher order association areas of the vision modality can be lost in occipital lobe lesions. What are the three important examples of these?

Answer 28

Some examples of visual agnosia include:

• object agnosia (from left occipitotemporal lesions),
• face agnosia or prosopagnosia (from right occipitotemporal lesions), and
• a failure to recognize the entirety of a visual array known as simultanagnosia (from bilateral occipitoparietal lesions).

Question 29

Visual agnosia does not mean the patient can’t see. What does it mean?

Answer 29

visual agnosia means that the visual image is seen normally but not adequately recognized

Question 30

unfortunately placed lesions or strokes can result in cerebral disconnection syndromes. What are the three examples talked about?

Answer 30

• conduction aphasia
• pure alexia
• corpus callosum lesions (selective anomia, agraphia, apraxia of the left hand)

Question 31

What’s up with pure alexia?

Answer 31

Another good example of disconnection is pure alexia, or alexia without agraphia, in which an affected person can write but not read.

• The lesion responsible for pure alexia is a stroke (usually) damaging the left occipital lobe and the splenium of the corpus callosum;
• this combination effectively disconnects the visual system from the language system, so that external visual input does not reach the left language cortex where it can be decoded, while the act of writing can still be performed

Question 32

What is Perseveration?

Answer 32

Perseveration - Continuation or recurrence of an activity without an appropriate stimulus; often seen with frontal lobe lesions.