Transcript The Brain
The Brain Lecture Overview • Methods of Studying the Brain • Structure of the Brain • Localization of Function • Brain Lateralization • Plasticity Studying the Brain • Study Brain Damage – Animal Studies – Cases of Human Brain Damage – TMS • Recording the Brain – EEG – Neuroimaging Brain Damage • In some animal studies, damage is produced in the laboratory. • But neuropsychologists often study naturally occurring cases of brain damage. • Transcranial magnetic stimulation (TMS): • Scientists can use TMS to study the effects of temporary brain damage. Recording the Brain • Techniques are used to study the whole brain: • Electroencephalography • Uses sensitive electrodes on the scalp to measure voltages produced by brain activity • Neuroimaging • CT, MRI, fMRI, PET scans Recording the Brain • MRI and CT scans • Study the brain’s anatomy—the size and location of individual structures • PET and fMRI scans • Reveal which brain locations are particularly active at any moment in time Recording the Brain • All these techniques make it clear that most activities rely on many brain sites. • Activities like reading or making decisions are supported by coordinated functioning of many different parts of brain. Brain Anatomy Brain Structure • The very top of the spinal cord forms the brain stem. • It includes the medulla and the pons. • Just behind these is the cerebellum. • The midbrain is on top of the pons, and on top of them all is the forebrain. The Cortex • The outer surface of forebrain is the cerebral cortex. • The cortex is a large, thin sheet of tissue crumpled inside the skull. • Some of the convolutions divide the brain into sections: • The frontal lobes, the parietal lobes, the occipital lobes, and the temporal lobes Left and Right Hemispheres • The brain is symmetrical around the midline. • Most structures come in pairs: • One on the left side • One on the right side Localization of Function • Different parts of the brain serve specialized functions • Sensory Information • Motor Control • Perception • Language • Planning and Social Cognition Cerebral Cortex • Some parts serve as projection areas: • The first receiving stations for information coming from the sense organs (e.g., somatosensory projection areas) • Departure points for signals going to the muscles (e.g., motor projection area) Cerebral Cortex • Adjacent sites in the brains usually represent adjacent parts of the body. • Assignment of space is disproportionate: • Usually the parts of the body that are most sensitive to touch receive the most space (in somatosensory projection area). • Parts of the body that we can move with more precision receive the most space (in primary motor projection area) Cerebral Cortex • Most projection areas have contralateral organization: – Left hemisphere receives information from right side of body (sensory), or controls right side of body (motor) – Right hemisphere receives information from left side of body (sensory), or controls left side of body (motor) Cortical Damage • Much of what we know about the cortex comes from studying brain damage. • Damage at identifiable sites can produce: • Apraxias (disorders in action) • Agnosias (disorders in perception) • Aphasias (disorders of language) • Disorders of planning or social cognition Apraxias • Difficulty in carrying out purposeful movements without the loss of muscle strength or coordination – Disconnection between primary and nonprimary motor areas – Able to carry out each part of a complex movement, but disruption lies in coordination of the movements Agnosias • Visual agnosia: disturbance in recognizing visual stimuli despite the ability to see and describe them • Prosopagnosia: inability to recognize faces (fusiform face area) – http://www.youtube.com/watch?v=vwCrxomPbtY&feature=related – http://www.youtube.com/watch?v=VKa-PuJCrO4&feature=related • Neglect Syndrome: complete inattentiveness to stimuli on one side of the body – http://www.youtube.com/watch?v=ADchGO-0kGo&feature=related • Akinetopsia: inability to perceive movement – “I see the world in snapshots – like frames of a move but most of the frames are missing” Aphasias • Broca’s Aphasia: disturbance in speech production, caused by damage to Broca’s area – http://www.youtube.com/watch?v=f2IiMEbMnPM • Agrammaticism • Anomia • Difficulty with articulation • Wernicke’s Aphasia: disturbance in speech comprehension, caused by damage to Wernicke’s area – http://www.youtube.com/watch?v=aVhYN7NTIKU&feature=relate d • Disruption in recognition of spoken words • Disruption in comprehension of the meaning of words • Inability to convert thought into words Disorders of Planning and Social Cognition • Caused by damage to prefrontal area – Disrupts executive control– processes that allow us to direct our own cognitive activities • e.g., setting priorities, planning, strategizing, ignoring distractors Lateralization • The left and right hemispheres are generally similar • However, the two hemispheres have specialized capacities – Left hemisphere: language – Right Hemisphere: visual and spatial tasks • The two halves of the brain work as an integrated whole – Communicate with each another through commissures • Split Brain Patients Other Split Brain Experiments http://www.youtube.com/watch?v=ZMLzP1VCA Plasticity • The brain is plastic—subject to alteration in the way it functions, such as: • Changes in the brain’s overall architecture • The central nervous system can grow new neurons: • But appears unable to do so with cortical injury • This promotes stability in the brain’s connections but is an obstacle to recovery from brain damage. Plasticity • Neurons are subject to alteration in the way they function, such as: • Changes in how much neurotransmitter a presynaptic neuron releases • Changes in neuron sensitivity to neurotransmitters • Creating new connections by growing new dendritic spines