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Cortex for Newbies
Neocortex
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
gray matter
(dendrites & synapses)
BANK
white matter
(axons)
FUNDUS
Brodmann’s Areas
Brodmann (1905)
• most common cortical map
• more recent schemes subdivide areas
• monkey and human areas are not
necessarily equivalent.
Lobes of cerebral cortex
Sulci and gyri maximize surface area - triples area of the brain
Cortical folding.
The degree of cortical folding is correlated with intelligence.
Cortical folding
http://brainmuseum.org/
Proportions of brain also differ across species
Cortical folding.
 The proportion of frontal cortex to the rest of the brain is also
thought to be correlated with intelligence.
ratio of frontal
to total cortex
0.3
0.2
0.1
lemur
gibbon
chimpanzee
human
But mammalian nervous systems are very similar
Fig 6.7
Species comparisons can yield insight into brain function
Specializations of the human brain
• larger representations of the hands
• neocortical specializations for speech
• extreme hemispheric specialization
• expanded prefrontal cortex
Interspecies Comparisons
Figure H shows the macaque monkey visual
areas morphed onto human cortex based on
the placement of sulcal landmarks (Van Essen
et al., 2001)
Can we assume humans are just morphed
monkeys?
In some areas the human cortical surface area
is slightly larger than in the macaque (e.g.,
visual cortex: 2X); in others it is considerably
larger (e.g., parietal cortex: 20X)
Are individual areas larger?
Are there more areas?
Maps in the Mind
Visual maps in the macaque
monkey brain
Visual maps in the human brain
derived from fMRI
The occipital lobe contains many maps of the visual world
Defining the lobes
frontal lobe
central (rolandic)
sulcus
parietal lobe
occipital
lobe
temporal lobe
sylvyan (lateral) fissure
Longitudinal Fissure
 also known as the
interhemispheric fissure as it
divides the two hemispheres
Midline structures of the brain
Visual Cortex
parieto-occipital sulcus
cuneus
lingual gyrus
calcarine sulcus
• 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.
Visual field defects.
Parietal Cortex
frontal lobe
parietal lobe
occipital
lobe
temporal lobe
Parietal Association Cortex
Primary somatosensory cortex: The region of the anterior parietal lobe
whose primary input is from the somatosensory system.
• integrates sensory information from multiple modalities
• integrating internal states (intentions, proprioception etc.) with external
information or goals (e.g., directing eye and hand movements)
• goal-relevant processing (macaque examples)
• left and right inferior parietal cortex play different roles
• left inferior parietal damage – apraxia
• right inferior parietal damage – neglect
• superior parietal cortex damage – optic ataxia, Balint’s syndrome
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.
Temporal Cortex
frontal lobe
parietal lobe
occipital
lobe
temporal lobe
Temporal Cortex
•
•
•
•
•
object and facial recognition (agnosia and prosopagnosia)
auditory processing
language – Wernicke’s area
Memory
emotional processing – the limbic system
Frontal Cortex
frontal lobe
parietal lobe
occipital
lobe
temporal lobe
Frontal Cortex – the “executive” brain!
• executive control – planning and guiding behaviour, judgement
• damage can lead to disorganized behaviour, disinhibition and
inappropriate social behaviour, impaired abstract thinking, rigidity
in thought, perseveration, personality changes, emotional lability
(inappropriate laughing or crying)
• not fully developed until late teens/early twenties
Primary motor cortex: The region of the posterior frontal
lobe that contains neurons that control movements of skeletal
muscle.
Contralateral Motor Control
RIGHT
LEFT
LEFT
RIGHT
LEFT
RIGHT
Left motor strip represents right sided motor control and vice versa.
Same organization for the somatosensory strip
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.