Kolb Ch. 17 LiNkI

• Different anatomically defined cortical lobes are each engaged in a wide range of cognitive activities
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• Although various lobes are engaged in different cognitive activities, they overlap remarkably in function

The cutting of cerebral connections

The ensuing behavioral effects due to disconnection

• Performed two disconnections on a Rhesus Monkey
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• All commisures were cut
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• Left amygdala was removed
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• Covered 1 eye with occluder and presented objects to the other eye
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• When objects are present to the eye ipsilateral to the ablated amygdala, monkey appeared “tame”
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• When objects were presented to the eye contralateral to the ablated amygdala, monkey appeared “wild”

• Information must be projected from the eye to the visual cortex, through the temporal lobes to the amygdala, and from the amygdala to the brain stem and frontal cortex, where autonomic responses, movements, and facial expressions, respectively, are activated
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• When the commisures between the two halves of the brain are disconnected, visual information from one eye can project only to the ipsilateral hemisphere
• If that hemisphere contains an intact amygdala, the circuits for activating species-typical behavior is complete
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• If that hemisphere does not contain an intact amygdala, visual information will be disconnected from motor systems and species-typical behavior cannot be elicited

His experiment would fail because information from one hemisphere could have crossed to the other, and each eye would have had access to the intact amygdala

• Association fibers
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• Projection fibers
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• Commissural fibers

• Can be distinguished as:
• Long fiber bundles that connect distant neocortical areas
• Short subcortical U-shaped fibers that connect adjacent neocortical areas

Includes ascending fibers from lower centers to the neocortex, such as projections from the thalamus, and descending fibers from the neocortex to the brain and spinal cord

• Functions primarily to connect the two hemispheres
• Include principally the corpus callosum, the anterior commisures, and the hippocampal commisures

• AKA Hard Body
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• Provides the major connections of neocortical areas
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• In humans, it is made up of 100 million to 800 million fibers
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• About half of these fibers are unmyelinated and quite small
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• Most, but not all, areas of the two hemispheres are connected

• Most of the primary visual cortex (Area V1) is devoid of interhemispheric connections, except for that part representing the midline of the visual world (Visual meridian)
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• Lack of such connections has been explained in functional terms
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• This cortex represents the visual world topographically, and there is no need for one half of the representation to be connected to the other
• The motor and sensory areas for the distal parts of the limbs (mainly the hands and feet) also lacks connections
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• Because their essential function is to work independently of one another, connections are not necessary
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• Monkeys have similar organization to humans, except that the motor connections appear to be more extensive in monkeys

• The density of projections is not homogeneous
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• Areas of the cortex that represents the midline of the body have the densest connections
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• Functional utility of this arrangement is that movements of the body or actions in central space require interhemispheric cooperation

Corpus callosum knit together the representations of the midpoints of the body and space that are divided by the longitudinal fissure

• Central meridian of the visual fields
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• Central meridian of the auditory fields
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• And trunk of the body on the somatosensory and motor cortex