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…
