10/14 - Function of Cerebral Cortex Flashcards
PHRENOLOGY
Spurzheim coined the term phrenology around 1800. It was one of the first attempts to localize specific functions and personality traits to different parts of the brain by feeling bumps on a person’s skull. This was further modified in 1883.
The premise was that traits that were dominant would have a larger representation in the brain and would thus produce a larger bump on the skull as it took up more space.
For example, if there was a large bump over the aggressiveness area the person could be violent.
The idea of localization was great. The “unscientific method” was not so great.
FUNCTIONAL LOCALIZATION IN THE CEREBRAL CORTEX
Based on a lot of research and observations of individuals with lesions in various parts of the brain, we know that there is very precise localization of different functions in specific parts of the cerebral cortex.
More advanced techniques, such as positron emission tomography or PET scan have provided even more validation for functional localization of sensory, motor and cognitive functions in the cerebral cortex.
FUNCTIONAL LOCALIZATION IN CEREBRAL CORTEX:
Sensory area
primary sensory area secondary sensory area
FUNCTIONAL LOCALIZATION IN CEREBRAL CORTEX:
Association area
parietal, occipital and temporal cortex:
conceptual elaboration of sensory data
prefrontal (frontal) cortex: judgement, foresight
FUNCTIONAL LOCALIZATION IN CEREBRAL CORTEX:
Motor area
primary motor area
secondary motor area
supplementary motor area
SOMATOTOPIC MAP - HOMUNCULUS
The somatosensory and motor cortex are very organized with respect to the body representation. This is referred to as the Homunculus. Specific parts of the body are represented in distinct areas.
Note: there is not a uniform area for all regions. In both the somatosensory and motor cortex, the face has a disproportionate representation as does the hand, especially the digits. This clearly reflects the sensitivity of these areas and the fine motor control. In comparison, the trunk has a very small representation.
Know the relative distribution of different regions of the body on the cortex!!
Basically, the body is draped over the primary motor and primary somatosensory cortices with the lower limb hanging over the top and into the cleft between the two hemispheres and the head resting on the temporal lobe.
In both the primary motor and primary sensory gyri, there is a very specific representation of the various parts of the body. Some areas have large representations (e.g., face in sensory cortex and hand in motor cortex) whereas other parts of the body have smaller representations (e.g., trunk).
Primary Motor Area
Precentral gyrus of lateral surface extending on to the upper part of this gyrus on medial side.
Immediately anterior is the premotor area which is involved in motor planning.
Input is from VL and VA nuclei of thalamus
Lesions to this area produce spastic paralysis. Unable to initiate voluntary movements.
COMPROMISING CIRCULATION IN THE ANTERIOR CEREBRAL ARTERY WOULD RESULT IN DEFICITS PRIMARILY IN _____.
COMPROMISING CIRCULATION IN THE ______ WOULD RESULT IN DEFICITS TO ALL OTHER AREAS OF BODY.
COMPROMISING CIRCULATION IN THE ANTERIOR CEREBRAL ARTERY WOULD RESULT IN DEFICITS PRIMARILY IN LOWER LIMB.
COMPROMISING CIRCULATION IN THE MIDDLE CEREBRAL ARTERY WOULD RESULT IN DEFICITS TO ALL OTHER AREAS OF BODY.
PREFRONTAL ASSOCIATION AREAS
There are two major Prefrontal Association areas.
One is dorsolateral. This area is involved in higher cognitive functions such as planning, insight, foresight and memory.
A second region is the ventromedial region. This region of the cortex has major connections with the limbic system and is involved in emotional responses.
PREFRONTAL ASSOCIATION AREAS:
Ventromedial region
Heavy interconnections with limbic system (emotions)
PREFRONTAL ASSOCIATION AREAS:
Dorsolateral region
Executive function, planning, insight, foresight, memory
Frontal Lobotomy
In the early part of the 20th century, a procedure was developed to deal with individuals with perceived aberrant personality disorders which involved taking a knife and severing the connections between the prefrontal cortex and the rest of the brain. This was called a frontal lobotomy.
Antonio Egas Moniz
PREFRONTAL LOBOTOMY
Surgically disconnect the prefrontal areas from the rest of the brain
Used to relieve severe psychotic depression
Lost ability to solve complex problems,
Unable to string together sequential tasks,
Unable to learn to do several parallel tasks at the same time,
Decreased level of aggressiveness.
Loss of ambition.
Inappropriate social responses.
Loss of morals.
Unable to carry through long trains of thought.
Usual patterns of motor activity without purpose.
It certainly did calm most patients down, but also left them completely flat personality-wise. These patients lost the ability to solve complex problems of to carry out sequential tasks. Other consequences included a loss of ambition, inappropriate social responses, loss of morals, inability to carry out long trains of thought and somewhat erratic motor activity. Fortunately, this is no longer used to treat patients with personality disorders.
What famous person had a frontal lobotomy?
President Kennedy’s sister did; she had been a combative person previously.
PHINEAS GAGE
The case of Phineas Gage is a classic example of a lesion to the prefrontal cortex. Phineas was a railroad worker who was tamping down explosives to clear an area to lay some track. The explosives detonated a bit early and drove the tamping rod through his eye socket and into his skull right though the prefrontal cortex.
Remarkably, Gage never lost consciousness, or quickly regained it (there is still some debate), suffered little/no pain, and was awake and alert when he reached a doctor 45 minutes later. He had a normal pulse and normal vision, and following a short period of rest, returned to work several days later. However, he was not unaffected by this accident.
Gage’s personality, reasoning, and capacity to understand and follow social norms had been diminished or destroyed. He illustrated little to no interest in hobbies or other involvements that at one time he cared for greatly. ‘After the accident, Gage became a nasty, vulgar, irresponsible vagrant. His former employer, who regarded him as “the most efficient and capable foreman in their employ previous to his injury,” refused to rehire him because he was so different.’
He survived the accident but was not the same man he was before the accident. He had no motor or sensory deficits, but his personality was completely changed.
Postcentral-Gyrus:
Other Names
Postcentral-Gyrus = Primary Sensory Cortex = S1
Parietal Lobe
Primary Sensory Cortex
More posterior gyri are sensory association areas: spatial orientation and directing attention.
Agnosia
inability to interpret sensations and hence to recognize things even though sense is intact
Tactile agnosia
Visual agnosia
Alexia
Auditory agnosia
Agnosia
inability to interpret sensations and hence to recognize things even though sense is intact
Tactile agnosia
Visual agnosia
Alexia
Auditory agnosia
I’m holding something in my hand that’s long and small… a pencil? a straw?
Apraxia
inability to perform particular purposeful actions
The inability to execute a voluntary motor movement despite being able to demonstrate normal muscle function.
The man “combing” his hair with scissors…
Diseases of the Parietal Association Areas
Agnosia: inability to interpret sensations and hence to recognize things even though sense is intact
Apraxia: inability to perform particular purposeful actions
Aphasia: Language Disorders
BROCA’S AREA
Essential for producing speech. Near face area of motor cortex.
Dr. Paul Broca’s patient called “Tan” (real name is Leborgne).
Inferior frontal gyrus of dominant hemisphere.
The patient Dr. Broca was studying has been given the code name Tan because that is the only word he could say. He could understand what was said to him, but when he tried to respond he was unable to form the proper words.
If Broca’s area is damaged, it produces motor aphasia.
WERNICKE’S AREA
Essential for interpretation of language. Near auditory cortex.
Superior Longitudinal Fasciculus
Intrahemispheric Pathway that Interconnects Core Language Centers
The area Carl Wernicke discovered was located in the junction of the parietal lobe and the temporal lobe. This is Wernicke’s area.
Given it’s relationship to the primary auditory cortex, damage to this region results in the patient’s not being able to recognize the spoken word. In some cases, if more of the visual cortex is involved, they may not be able to recognize written words which is called alexia. Patient’s with receptive aphasia can hear perfectly well. However, words sound like gibberish to them and they cannot interpret what is being said. There is a distinct fiber tract that connects Broca’s and Wernicke’s areas. This is the Superior longitudinal fasciculus or the Arcuate fasciculus.
Wernicke’s aphasia is what type of aphasia?
receptive aphasia
Broca’s aphasia is what type of aphasia?
Motor aphasia
intrahemispheric pathway
connects two regions on the same side of the brain.
LANGUAGE AREAS
Lesions in different parts of the language centers produces very different symptoms.
If the lesion is confined to Wernicke’s area the patient wil have a defect in comprehending speech, but will be able to speak normally.
Other forms of receptive aphasia include anomic aphasia which is an inability to find the right word when speaking.
If the lesion is confined to Broca’s area, the patient will understand what is said to them but would not be able to repeat it. Often times they try to speak but it comes out unintelligible or they repeat the same word, as Dr. Broca’s patient who just said tan for everything.
If the lesion involves the superior longitudinal fasciculus they have conduction aphasia. They may understand what is said, and they could speak spontaneously; but they would not be able to repeat a word that was spoken to them as the link between hearing and speaking is broken. The spontaneous speech may or may not have anything to do with an ongoing conversation.
Finally, if both areas and the pathway are damaged the patient would have global aphasia in which there would be poor comprehension and an inability to repeat a word.
Sensory Language Area:
(Wernike’s area) Receptive Aphasia
Defect in comprehension, good spontaneous speech
Anomic Aphasia - word finding difficulty
Motor Language Area:
Broca’s area
Motor Aphasia - Good comprehension, no speech or just gibberish
Superior Longitudinal Fasciculus
Conduction Aphasia
Good comprehension, good spontaneous speech
Poor repetition
Simultaneous Deficits in both Broca’s area and Wernicke’s area
Global Aphasia
Poor repetition
No Comprehension
CEREBRAL DOMINANCE (LATERALIZATION, ASYMMETRY)
Dominant Hemisphere: Language – speech, writing
Calculation
Non-dominant Hemisphere:
Spatial Perception (3D subject)
Singing
Playing musical instruments
CEREBRAL DOMINANCE (LATERALIZATION, ASYMMETRY)
Dominant Hemisphere: Language – speech, writing
Calculation
Non-dominant Hemisphere:
Spatial Perception (3D subject)
Singing
Playing musical instruments
Although the cerebral cortex appears homogeneous, there are some functional asymmetries. The dominant hemisphere, which is the left hemisphere for right handed individuals, is mostly involved in language and calculations. The non-dominant hemisphere is better at spatial perception and singing including playing a musical instrument.
Dominant Hemisphere
Language
– speech, writing
Calculation
Non-dominant Hemisphere
Spatial Perception (3D subject)
Singing
Playing musical instruments
Occipital Lobe
Parieto-occipital fissure (red)
-very deep
-best seen from midsagittal view
Defines border with parietal lobe
Calcarine sulcus (blue) -contains Primary visual cortex (V1)
Cuneus (pink)
-visual areas on medial side above calcarine fissure (lower visual field)
Lingual gyrus (yellow) -visual areas on medial side below calcarine (upper visual field)
Parieto-occipital fissure
-very deep
-best seen from midsagittal view
Defines border with parietal lobe
Calcarine sulcus (blue)
-contains Primary visual cortex (V1
Cuneus (pink)
-visual areas on medial side above calcarine fissure (lower visual field)
Lingual gyrus (yellow)
-visual areas on medial side below calcarine (upper visual field)
WHAT AND WHERE PATHWAYS
Connections between association areas of visual cortex and parietal lobe (where) and temporal lobe (what).
Dorsal pathway has been found to be more complex and represents a widespread visuospatial processing system that contributes to both spatial perception and non-conscious spatial processing across numerous cortical areas in the frontal, temporal and limbic lobes.
Dorsal pathway has been found to be more complex and represents a widespread visuospatial processing system that contributes to both spatial perception and non-conscious spatial processing across numerous cortical areas in the frontal, temporal and limbic lobes.
There is a projection from association areas of the occipital lobe to the posterior parietal cortex. From there multiple pathways arise and project to:
Premotor area of frontal lobe:
essential for visually guided movements
Prefrontal area of frontal lobe:
essential for spatial working memory
Medial temporal lobe:
essential for navigation
Premotor area of frontal lobe:
essential for visually guided movements
Prefrontal area of frontal lobe:
essential for spatial working memory
Medial temporal lobe:
essential for navigation
A lesion of the posterior parietal area can lead to Neglect syndromes.
A deficit resulting from cortical lesions that causes the observer to ignore part of visual space.
This deficit can be egocentric (person as reference), as in hemispatial neglect (in which one half of the visual field is ignored), or allocentric (for example, when the left side of all objects is ignored).
VISUAL ASSOCIATION AREAS
V4 (color)
Face recognition
Perceive Facial Expression
Ventral = “what”
Dorsal = “where/how”
