Module 13.1: Lateralization of Function Module 4.3: Plasticity after Brain Damage

The Left and Right Hemispheres Commissure, a set of axons that connects the hemispheres: Corpus callosum Anterior commissure Hippocampal commissure

Lateralization: Division of labor between the two hemispheres

Visual Field: What is visible at any moment Left and right visual fields: Each processed in contralateral hemisphere Optic chiasm: where crossover of info occurs Visual Connections to the Hemispheres

Auditory Connections: Each hemisphere gets information, but contralateral hemisphere pays more attention Auditory Connections to the Hemispheres

Cutting the Corpus Callosum Epilepsy: A condition involving excessive, synchronized neural activity Seizure: Behavioral symptom, can range from mild to severe Focus: Point in brain where seizure begins Commissurotomy: Severing of the corpus callosum Split-brain patient: has undergone a commissurotomy “Severed Corpus Callosum” video clip (10m): watch?v=lfGwsAdS9Dc

Functions Associated with the Hemispheres

Development of Lateralization and Handedness Planum temporale: Critical for speech comprehension Larger in left temporal lobe of 65% of people Maturation of the corpus callosum: Occurs gradually over time Young children have more difficulty coordinating limbs

Plasticity After Brain Damage Survivors of brain damage show subtle to significant behavioral recovery. Video clip from “The Secret Life of the Brain, The Aging Brain” (2002):

Plasticity After Brain Damage Possible causes of brain damage include: tumors infections exposure to toxic substances (a) Brain of a person who died immediately after a stroke. Note the swelling on the right side. (b) Brain of a person who survived for a long time after a stroke. Note the cavities on the left side, where many cells were lost. (c) Brain of a person who suffered a gunshot wound and died immediately. degenerative diseases closed head injuries stroke

Plasticity After Brain Damage Stroke (cerebrovascular accident, CVA): –temporary loss of blood flow to the brain –common cause of brain damage in the elderly Types of strokes include: Ischemia -most common type of stroke Hemorrhage -less frequent type of stroke

Plasticity After Brain Damage Ischemia and hemorrhage also cause: Edema-the accumulation of fluid in the brain –increases pressure on the brain –increases the probability of further strokes –kills neurons

Treatments after Stroke Tissue plasminogen activator (tPA) breaks up blood clots and reduces the effects of ischemic strokes. Cooling brain (91-97°F): –less activity –lower energy needs –less risk of overstimulation Cannabinoids –minimize cell loss after brain damage by decreasing the release of glutamate. –Excess glutamate may result in the over-excitation of neurons

Plasticity After Brain Damage Diaschisis refers to the decreased activity of surviving neurons after damage to other neurons.

Plasticity After Brain Damage Damaged axons do grow back under certain circumstances. PNS axon grows back at a rate of about 1 mm per day.

Plasticity After Brain Damage Collateral sprouts are new branches formed by other non- damaged axons that attach to vacant receptors.

Plasticity After Brain Damage Denervation supersensitivity- the heightened sensitivity to a neurotransmitter after the destruction of an incoming axon and usually a result of increased receptors.

Plasticity After Brain Damage Phantom limb refers to the continuation of sensation of an amputated body part and reflects this process. The cortex reorganizes itself after the amputation of a body part by becoming responsive to other parts of the body.

Plasticity After Brain Damage Phantom limb can lead to the feeling of sensations in the amputated part of the body when other parts of the body are stimulated.

Plasticity After Brain Damage Deafferenated limbs are limbs that have lost their afferent sensory input.