Lecture 5 - Cortex Flashcards
The Cortex
- Cortical folding and intelligence
- Brain size and evolution
- Cortical Topography
- Cortical Function
What is the neocortex?
Gyri and Sulci
Gyri
(plural: singular = gyrus) – convolution or bump – protruding rounded surfaces (folds)
Sulci
(plural: singular = sulcus) – valley between gyri or enfolded regions that appears as surface lines (gaps between gyri)
Fissure
very deep sulcus
What does sulci and gyri do?
Sulci and gyri maximize surface area - triples area of the brain.
What is cortical folding correlated with?
The degree of cortical folding is correlated with intelligence.
Across species do humans have more neocortex?
yes
The proportion of frontal cortex to the rest of the brain is also thought to be correlated with ______
intelligence
Mammalian NS’s are very similar. Species comparisons can yield insight into…
brain function
- humans are more vision based
- similar common areas
Specializations of the human brain
- larger representations of the hands
- neocortical specializations for speech
- extreme hemispheric specialization
- expanded prefrontal cortex
What does cortex look like?
very layered
- layers are cell differenciations
Cytoarchitecture
the cellular composition of a bodily structure
Cortical layers
- Grey matter is made up of non-myelinated cells that have a layered appearance in cross section according to different cell types and groupings.
- 6 layers but size and shape of cells and thickness of layers differs across brain regions.
- motor cortex & sensory cortex with 6 layers each
Central (Rolandic) sulcus
splits frontal & parietal lobe
Lateral (Sylvian) fissure
splits horizontally temporal from frontal/parietal lobe
Longitudinal Fissure
AKA the interhemispheric fissure as it divides the 2 hemispheres
Corpus Callosum
Thick band of nerve fibres that connect the left and right hemispheres.
- biggest fiber tract
- used DTI
What is pre & post the central sulcus?
pre - motor cortex
post - somatosensory cortex
Brodman’s areas
- Cytoarchitectonically defined regions (assigned numbers).
- Cytoarchitectonics – cellular organization differs across regions.
Cortical Topography
- Cortical topography refers to the practice of ‘mapping’ functions (e.g., motor control) onto specific regions of the brain.
- Hughlings Jackson – first noticed that specific body parts were involved in specific epileptic seizures – the Jacksonian march.
- Proposed a “map” of the body in the brain – the homunculus.
Hughlings Jackson
first noticed that specific body parts were involved in specific epileptic seizures – the Jacksonian march.
“Map” of the body in the brain
the homunculus
Describe motor & somatosensory strips
- Fine motor & ability to speak & talk takes a lot of motor movements (larger representation on motor cortex)
- Lips, tongue, fingertips have a larger representation on somatosensory cortex
- areas that are involved in delicate, fine sensory touch get more space
- feel more delicate touches on fingertips than back
- receptive fields are so densely packed on finger tips that you could tell it was 2 separate things touching you - if 2 prongs are close
- receptive fields are larger in back so harder to distinguish b/t 2 v. closely related touches so you report as 1
Why do the hand and face regions “get” more cortex than other regions?
more fine motor control or more touch receptors than other areas.
More sensitive the area…
the more involved in fine motor control, the more brain real-estate it gets
The Penfield Map – cortical topography
Brain mapping
Penfield did brain mapping
- stimulated various areas of brain & saw what it stimulated
Phantom limb and the Penfield map
- Limb amputation often leads to PHANTOM LIMB pain.
- The phantom limb can be mapped onto the face (Ramachandran).
- Hand representation actually next to chin (Servos - fMRI).
- probably due to fetal position (Farah).
- same would be true for feet and genitals being close together.
Occipital Lobe
vision
- upper bank of calcarine (cuneus) – lower visual field.
- lower bank of the calcarine (lingual) – upper visual field.
Retinotopy
mapping the visual world onto the visual cortex.
Fovea
region on back of retina that is v. packed with higher acuity receptors (sharp vision happens)
As we move out into the periphery, we can have…
much larger areas of periphery mapped onto a relatively smaller section of brain
Why is periphery in less focus?
we don’t need to see perfect acuity in periphery - we just need to see movement
Areas of brain that are more higher acuity…
got more real-estate devoted to them (larger section of cortex)
Visual field defects.
Scotoma - blind spot
Quadrantanopia - loss of vision in a quarter of the visual field
Hemianopia - loss of vision in half of the visual field
Parietal Lobe
“responsible for processing somatosensory information from the body; this includes touch, pain, temperature, and the sense of limb position.”
Parietal Association Cortex
- integrates sensory information from multiple modalities.
- goal directed actions.
Superior parietal cortex damage result in…
optic ataxia, Balint’s syndrome.
problems in visually guided movements
Left and right inferior parietal cortex play different roles:
- left inferior parietal damage – apraxia. (difficulty with hand movements)
- right inferior parietal damage – hemispatial neglect. (half of visual world is missing)
Somatosensory cortex (within parietal lobe)
concerned with the conscious perception of touch, pressure, pain, temperature, position, movement and vibration.
Hemispatial Neglect
- damage to the right parietal lobe often results in a failure to attend to or represent information appearing on the left side of space despite intact sensory processing and visual acuity.
- debilitating in every day life.
- unable to construct adequate representations of the left side of space. (like their ignoring left side)
Olive Sacks - noticed someone only ate half of plate
- only saw half portion so he suggested for her to spin to see other side of food
Olive Sacks
- noticed someone only ate half of plate
- only saw half portion so he suggested for her to spin to see other side of food
Temporal Lobe
“processing affect/emotions, language, and certain aspects of visual perception.”
Temporal Cortex
- auditory processing
- language – Wernicke’s area
- object and facial recognition (agnosia (inability to recognize objects) and prosopagnosia (inability to recognize faces))
- Memory
- emotional processing – the limbic system
Primary auditory cortex:
The region of the superior temporal lobe whose primary input is from the auditory system.
Insular cortex:
A sunken region of the cerebral cortex that is normally covered by the rostral superior temporal lobe and caudal inferior frontal lobe.
Frontal Lobe
the “executive” brain!
- executive control – planning and guiding behaviour, judgement.
- not fully developed until late teens/early twenties.
Damage to Frontal Cortex
damage can lead to personality changes, disorganized behaviour, disinhibition and inappropriate social behaviour, rigidity in thought, emotional lability (inappropriate laughing or crying).
Phineas Gage and the Frontal Cortex.
- injured by a tamping iron piecing his skull – probably affected both frontal lobes to some degree (perhaps left > right).
- recovered but wasn’t the same.
- became socially inappropriate, had difficulty maintaining a job. (diff. personality - had outburts (rude & impatient)
- eventually became a sideshow attraction in Barnum and Bailey’s Circus (actually traveled with the tamping iron that had caused his injury).
Primary motor cortex:
The region of the posterior frontal lobe that contains neurons that control movements of skeletal muscle.
Contralateral Motor Control
- left motor strip represents right sided motor control and vice versa.
- same organization for the somatosensory strip.
Association Cortex
Sensory association cortex
Motor association cortex
Sensory association cortex:
Those regions of the cerebral cortex that receive information from regions of the primary sensory cortex.
Motor association cortex:
The region of the frontal lobe rostral to the primary cortex; also known as the premotor cortex.
A bulge located between the adjacent grooves in the surface of the human cortex would be termed a A) fissure. B) gyrus. C) cerebral aqueduct. D) ventricle. E) sulcus.
B) gyrus.
After sustaining a stroke involving the right parietal lobe, Mr. M continued to show problems in A) understanding speech. B) producing speech. C) repeating words. D) moving his right arm and leg. E) grasping an object on the left.
E) grasping an object on the left.
area involved in goal directed movements
The planning and execution of movements is a function performed by association cortex in which cortical lobe? A) occipital B) frontal C) temporal D) insular E) parietal
B) frontal
Damage to the occipital cortex may result in which of the following?
A) problems in naming a song they knew before sustaining brain damage
B) difficulty in playing a tune on a piano
C) difficulty in naming an object the person can touch (but not see)
D) problems in recognizing an object by sight
E) an inability to recognize a familiar odor
D) problems in recognizing an object by sight
Which of the following would be expected as a result of damage to the somatosensory association cortex?
A) problems in recognizing an object by sight
B) difficulty in playing a tune on a piano
C) difficulty in naming an object the person can touch (but not see)
D) problems in naming a song they knew before sustaining brain damage
E) an inability to recognize a familiar odor
C) difficulty in naming an object the person can touch (but not see)
