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Cortex for Newbies
Neocortex
• 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
The Neocortex - Gyri and Sulci.
gray matter (dendrites & synapses)
white matter (axons)
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Brodmann’s Areas
• most common cortical map• more recent schemes subdivide areas• monkey and human areas are not necessarily equivalent.
Brodmann (1905)
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.
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
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otal
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lemur gibbon chimpanzee human
0.1
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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 ComparisonsFigure 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
The occipital lobe contains many maps of the visual world
Visual maps in the macaque monkey brain Visual maps in the human brain
derived from fMRI
Defining the lobes
frontal lobe
temporal lobe
occipitallobe
sylvyan (lateral) fissure
central (rolandic) sulcus
parietal lobe
Longitudinal Fissure
also known as the interhemispheric fissure as it divides the two hemispheres
Midline structures of the brain
Visual Cortex
• upper bank of calcarine (cuneus) – lower visual field• lower bank of the calcarine (lingual) – upper visual field
calcarine sulcus
parieto-occipital sulcusparieto-occipital sulcus
cuneus
lingual gyrus
Retinotopy – mapping the visual world onto the visual cortex.
Visual field defects.
Parietal Cortex
frontal lobe
temporal lobe
occipital
lobe
parietal lobe
Parietal Association Cortex
• 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
Primary somatosensory cortex: The region of the anterior parietal lobe whose primary input is from the somatosensory system.
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.
• Unable to construct adequate representations of the left side of space.
• debilitating in every day life
Temporal Cortex
frontal lobe
temporal lobe
occipitallobe
parietal 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
temporal lobe
occipitallobe
parietal 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
Left motor strip represents right sided motor control and vice versa.
Same organization for the somatosensory strip
LEFT RIGHTLEFTRIGHT LEFT RIGHT
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.
