PSYC 311 Lecture Notes - Lecture 10: Piriform Cortex, Angular Gyrus, Somatosensory System
8 Jun 2018
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Wednesday, May 17th, 2017
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PSYC 311
Week 3 Lecture 10: somatosensory and apraxia
Today’s leture ill ot e o midterm
- Even today, people still incorrectly name post- central gyrus the S1(primary sensory
cortex), because the macrosimulation (by Dr. Penfield) is not precise
- On the post-central gyrus, there were three distinct cytoarchitectonic areas:
o If we take the central sulcus and open it up, we notice area 4 is at the anterior
bank of the central sulcus
o Area 3 is on the posterior bank of the central sulcus
o Area 1: gyrus of the post central
o Area 2 is on the anterior bank of the post-central sulcus
- S2 is another somatosensory area: upper bank of Sylvian Fissure: parietal operculum
o In the 1950s: we have a concept of more than one somatosensory area.
- How is this finding relate to the three distinct cytoarchitecture areas in post central
gyrus/sulcus?
o In the late 1950s, early 1960, Kass explores the above question
▪ They use a tiny electrodes and to stimulate one neuron. With
microstimulation, they can stimulate precise region.
o They discover three separate and mirror-image somatosensory maps (area 3,1,2)
in post central gyrus. It is interesting because S1 of Dr. Penfield are actually three
separate somatosensory maps.
o Why do we have three distinct areas? Which of these are primary
somatosensory cortex?
▪ Nowadays we consider area 3 to be primary somatosensory cortex, why?
• Because it has the characteristics of primary cortical areas: first
CORTICAL area to receive somatosensory information
• Note: It is not the first area to receive somatosensory information
in the brain, The information that comes to primary cortical areas
are already processed by subcortical areas.
- Reasons we consider area 3 is primary somatosensory cortex:
Economo gives us the precise definition of primary somatosensory area:
o In these areas because their role is to receive subcortical information, layer 4
which receives information from subcortical areas increases.
o Layer 4 has small axons, they receive information within the cortex, they don't
have to distribute. They look very granular, lots of dusts: koniocortex
o Koniocortex appearance can also be seen in V1, or any primary cortex
o Area3 gets information, only needs to send it to its neighbor area 1 and 2,
therefore, they do’t eed large euros i layer ad 5; however, for area 1
and 2, they have bigger neurons in layer 3 and 5 because they have to
communicate with further areas
o Conclusion: because area 3 has huge layer 4, therefore, it is defined as the
primary somatosensory cortex
- In the primary somatosensory cortex, we have a VERY PRECISE representation/map of
the body
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Wednesday, May 17th, 2017
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o Tiny little neurons that present specific part of the body
o Koniokortex (millions of neurons) represents of the external world in a very
precise somatotopic way.
- Neurocomputation:
o Your hand is represented by 100 million neurons, each one knows nothing about
what others (not neighbors) are doing
o That means all the neurons converged their information to one neuron; when
that neuron sends action potential, it is combining all the information from one
finger. If these neurons combine again, and sends to another one neuron, to
represent one hand. However, that is still not enough, in order to have the whole
body image, you need information from visual, somatosensory, auditory cortical,
and you get an integration of information.
o These biological principal by integrating information, you are building a
representation of your world/ body.
o in PF-> neuron integrates information
- Why do we have area 3, area 1 and area 2?
o The properties of these neurons in those three areas are different.
▪ Area 3: responding continuously, as long as the stimulus is applied.
▪ Area 1: responding to vibration
▪ Area 2: getting information subcortically and area 1, sensitive to shape
o Study carried out by Semmes:
▪ They try to make tiny lesions in monkeys: they are trained to do varies
somatosensory tasks, and see their response:
• Lesion in area 3: loss sensation
• Lesio i area : a’t tell vibration
• Lesio i area : a’t tell if the ojet is sall or ig
- SMA: located at medial area 6
o Horizontally see leg arm face representation
o S1 is a functional term
- Apraxia: a concept rose in late 1900 century by Lipmonn
o Praxis: action -> apraxia: problems in action
o Geschwings gave a standard definition of apraxia:
o Patient was asked to salute: patiet a’t salute but waving; patient however
knows the concept of salute. The patient fails to produce that action.
o Lipoo aes this “ideomotor apraxia” (it is a disconnection syndromes)
▪ The separation of the idea from the action
▪ Another example of disconnection syndrome: you know what salute is,
but fail to carry out the action
o Aordig to Geshig: the patiet opreheds ith the Werike’s region,
but fails to relay it to motor area.
o You would expect them to have conduction aphasia.
o Lipmoon found another problem (ideational apraxia):
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