Download Nolte Chapter 22: Cerebral Cortex

Nolte Chapter 22: Cerebral Cortex
Onset of gyrification is mid gestation, after completion of neuronal proliferation and
migration. Occurs in a lateral to medial gradient.
Almost all of the cortex is neocortex. Paleocortex covers the base of the
telencephalon. Most of the hippocampus is archicortex.
Puramidal cells are the most numerous neurons of the neocortex and have a conical
cell body from which dendrites emerge but a long apical dendrite ascends vertically
and a series of basal dendrites spread out horizontally. Pyramidals can go all the
way to spinal cord. Internurons usually stay in cortex. Nonpyramidal just modulate
pyramidal. Basket are at soma and dendrites. Chandelier are at axons.
Dendritic spines may be the sites of synapses that are selectively modified as a
result of learning. Small changes in their geometry can cause relatively large
changes in its electrical or diffusional properties and therefore in the efficacy of that
synapse.
Neocortex has 6 layers. Most superficial is cell poor molecular. The deepest is
polymorphic and populated mainly be fusiform shaped modified pyramidals.
The lack of stellate (granule cells) yields the name “agranular”. Sensory areas do not
have many long projections so they are more “granular” or “koniocortex”. Motor
does. These exceptions are heterotypical as compared to the homotypical, clear 6
layers parts of cortex. Agranular heterotypical is the thickest and granular
heterotypical is thinnest.
Afferents from the same hemisphere are association fibers. From the other are
commissural fibers.
Thalamic relay nuceli primarily end in Layer IV.
Intralaminar go to VI.
Other cortical/subcortical layers communicate to eachother via II and III.
III is the major source of corticocortico fibers.
Layer V projects to brainstem and spinal cord
VI are regulatory back to the thalamus.
I is rich in axons and dendritic tufts and some horizontal cells.
Superior longitudinal fasciculus (aka arcuate) is above the insula between the
frontal lobe and posterior portions of the hemisphere, where it fans out among the
parietal, occipital, and temporal lobes.
Superior occipitofrontal connects frontal and superior parts of parietal and occipital.
Travels parallel to the corpus collosum.
Subcollasal fasciculus connects cortical areas to caudate.
Uncinate is an association bundle that hooks around the margin of the alteral sulcus
to interconnect the orbital cortex and anterior temporal cortex
Cingulum is within the cingulate gyrus and continues around the parahippocampal
gyrus in almost a complete circle.
Inferior Longitudinal fasciculus connect superior temporal with insula, oribital, and
prefrontal.
The cortex is organized in vertical slabs where each column has paramaters that are
constant for all cells. Oculuar dominance, tonotopy in A!, etc.
BA3(S1) received most of thalamic input from VPL and VPM. 1 and 2 receive
progressively less and their receptive fields become more complex.
It is hard to elicit pain by stimulation of the postcentral gyrus, but damage does
result in an inability to locate a painful stimulus. Pain seems to be confined to
S2(parietal operculum buried in lateral sulcus), insula, and anterior cingulate. These
last two allow for the feeling for the unpleasantness of pain.
V1(BA17) is known as striate cortex. Peripheral parts are represented anteriorly
and the fovea has a large representation posteriorly. The vertical meridian is
presented along the upper and lowe borders of area 17. Visual association (18 and
19) take up the rest of occipital. These association also receive input from superior
colliculus-pulvinar pathway.
Loss of primary visual cortex results in loss of conscious awareness of visual stimuli.
It is useful for combining inputs from both eyes to perceive depth. Association adds
in color and other elaborative parameters.
Visual is also termed striate because of the pronounced band of white matter fibers
in Layer IV called the stria of Gennari.
Ventral where. Dorsal what.
Lingual gyrus is below the calcarine sulcus.
Area 41 in the lateral sulcus is Heschel’s gyrus and is granular and tonotopically
organized. 42 is A2 and surrounds Hescl. Auditory information is represented
bilaterally and damage to one side usually only results in trouble localizing sound.
Prjections to prefrontal appear to form at least 2 auditory processing streams.
Spatial stream originates in caudal part of SFG and projects to parietal and
prefrontal. Pattern/object stream originates in the anterior part o the lateral belt.
Vestibular has a place along the superior temporal gyrus and posterior insula.
Premotor cortex has a higher threshold for movements and likely involves larger
groups of movements. SMA responsible for planning and fine motor coordination
alongside cingulate motor.
Language deficits are more left hemisphere. The left hemisphere is typically rhe
dominant one independent of handedness.
The temporal plane is larger on the left.
Broca’s area is in the opercular and triangular parts of the IFG.
Wernicke’s is in the posterior part of the superior temporal gyrus.
Together Broca’s and Wernicke’s are the perisylvian language zone.
Inability to use language is known as aphasia.
Broca’s aphasics can produce few words and tend to leave out all but the most
meaningful words, but have less difficulty comprehending speech. Their word
finding is difficult and speech sounds frustrating.
Wernicke’s aphasics are able to produce written and spoken words but the
sequences are defective in their linguistic content. There may be substituions of one
letter or word for another (paraphasia) or stringing together phrases in an order tha
convey little or no meaning (jargon aphasia). Wernicke’s aphasics are deficient in
the comprehension of language. They have a nice flow to their words but they are
devoid of useful content and filled with a lot of vague terms.
Broca’s is responsible for generation of language and wernicke’s for formulation of
language. Destruction of Broca’s would deprive the motor cortex of instructions
needed to generate language but leave the muscles able to participate in other
activities. Wernicke’s would leave Broca’s area unchecked so that words would be
produced without reagard for their meaning. This could also happen with
destruction of the arcuate (which connects the two), but this lesion would leave
comprehension in tact and result in “conduction aphasia” where subjects can
understand words but not repeat them.
The rhythmic and musical aspects of speech are called prosody and controlled by
the right hemisphere. Right IFG produces prosody and the right posterior
temporoparietal region comprehends it.
Sensory specific agnosia is the inability to recognize the identity or some other
property of objects when using a given sense even when that sense is intact.
Interrelated multimodal areas are centered on the intraparietal sulcus and keep
track of shifting relationships between body parts and things in the outside world,
factoring in motivation, attention and the relevance of different objects. The parietal
eye fields monitor the relationship between eye position and not just visual objects,
but also sound sources and body parts.
Frontoparietal circuits switch attention.
Removal of posterior parietal cortex causes neglect of contralateral half of the body
and the limbs go unused and reaching with them is inaccurate. Contralateral neglect.
Right hemisphere is dominant in spatial attention. After left hemi damage the right
can direct attention to both contra and ipsilateral sied but after right damage, left
can only attend to the contralateral side, so the left side of the world is neglected.
Apraxias are the inability to perform some actions. Damage to parietal association
renders someone unable to follow instructions to touch nose, but can do it to reach
for an inch.
Anterior to BA 4 and 6 is prefrontal cortex which is centrally involved in the
controlling of activities (executively) of other cortical areas. It receives input from
the dorsomedial nucleus of the thalamus.
DLPFC has interconnections with parietal multimodal cortex and somatosensory,
visual, and auditory association areas. It’s implicated in working emmory
VMPFC is interconnected with limbic structures and associated with impulse
ocontrol. Phineas Gage personality changes after damage here.
Splitting the corpus collosum and presenting words to the left visual field cannot be
read.
Left language. Right space.
Disconnection syndromes cause strange deficits. Alexia without agraphia is the
ability to write but not read. Destruction of the left visual cortex and splenium of
corpus collosum causes language areas of left hemispheres to be cut off from visual
input and right visual is cut off from left language areas. But motor is fine and actual
language are fine…
Projection fibers are the likes of the corona radiate and corticospinal tract.
Commissural are like anterior commissure and corpus calllosum
Association fibers are more like the Uncinate, IFOF, cingulum, fornix, stria
temrinalis, etc.
Priuimary gustation is frontal operculum and anterio insula where taste comes for
nucleus of the solitary tract through the thalamus VPM.
Olfactory is pelocortex and includes all the targets of the olfactory bulb and is the
piriform cortx just medial to amygdala.
Unimodal association is one sense and expanded. Multimodal is many senses and
higher-level of their combination.
Frontal association is reasoning. Parietal is motor and visual integration. Temporal
is speech and memory.
Inferior parietal lobule inclused supramarginal and angular and these process
auditory, visual, and somato information and particupates in higher language and
other processes involving sensory integration. Rostral portion is mirror neurons,
middle is attention and rules, and caudal is emantic and phonological processing.
Superior Parietal Lobule is a visual, auditory, and somato integration area that is
responsible for hand-eye coordination and forms part of the dorsal visual
processing stream.
Gerstmann’s syndrome can’t tell which finger they are holding up. They have right
left confusion, agraphia, acalculia. Typicallly seen with damage to left angular gyrus.
Foix Chavany Marie syndrome partial paralysis of face, pharync and jaw with
damage to operculum. Can make involuntary movements like smiling, eating, or
blinking eyes.
Frontal aslant tract connects Broca’s with anterior cingulate and pSMA.
Frontal 4 – M1
6 – Premotor
44/45 (on left) – Broca’s
3,1,2 – S1
5,7 – Somato association
17- V1
18/19- Visual Association, V2345
41- Auditory A1