Transcript Lecture 2
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.