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Chapter 2 The Brain The Brain Technology to Study the Brain • Electroencephalograph (EEG): • records “waves” of electrical activity in the brain using metal electrodes • Computerized axial tomograph (CAT): • thousands of X-ray photos of the brain are combined to form a crosssectional picture • Magnetic resonance imaging (MRI): • produces three-dimensional images of the brain’s soft tissues by detecting magnetic activity from nuclear particles in brain molecules Technology to Study the Brain • Positron emission tomography (PET): measures neural activity in different brain regions over several minutes by monitoring sugar glucose consumption • Functional magnetic resonance imaging (fMRI): measures neural activity in different brain regions averaged over seconds by monitoring blood oxygen levels PET Scan MRI Scan Three Major Brain Regions • Their names come from their physical location in the human embryo. – Hindbrain: Located above the spinal cord, – Midbrain: Located above the hindbrain – Forebrain: Located above the midbrain Development of the Brain Three Major Brain Regions: Hindbrain • Hindbrain consists of: – Medulla: controls breathing, heart rate, swallowing, digestion, and posture – Pons: associated with sleep and arousal – Cerebellum: regulates and coordinates body movement and may play a role in learning The Cerebellum Midbrain Reticular formation: regulates and maintains consciousness – plays an important role in controlling arousal Forebrain Controls complex emotional reactions, cognitive processes, and movement patterns. Consists of: – Thalamus: the brain’s sensory relay station – Limbic system: influences fear, aggression, and new memories – Cerebral cortex: located on top of these structures; the most complex part of the brain Thalamus • Brain’s Sensory Switchboard • Directs incoming information from the sensory systems (except smell) to the appropriate location on the cortex. The Brainstem and Thalamus Limbic System • a doughnut-shaped system of neural structures at the border of the brainstem and cerebral hemispheres • associated with emotions such as fear and aggression and drives such as those for food and sex • includes the hypothalamus, hippocampus and amygdala The Limbic System Hypothalamus • neural structure lying below (hypo) the thalamus • directs several maintenance activities • eating • drinking • body temperature • helps govern the endocrine system via the pituitary gland • linked to emotion Hippocampus • Structure linked to the processing/formation of new explicit memories • Manufactures new neurons Amygdala [ah-MIG-dah-la] – two almond-shaped neural clusters that are components of the limbic system and are linked to emotion, especially rage and fear The Limbic System • Electrode implanted in reward center Main Parts of the Human Brain Lobes of the Cerebral Cortex • The cerebral cortex is divided into two rounded halves, called the cerebral hemispheres. – These hemispheres are connected together at the bottom by the corpus callosum. – Both hemispheres are divided into four major sections called lobes: The Brain The Cerebral Cortex Cortical Localization • Occipital Lobes – include the visual areas, each of which receives visual information from the opposite visual field • Temporal Lobes – include the auditory areas, each of which receives auditory information primarily from the opposite ear Visual Cortex • Functional MRI scan of the visual cortex activated by light shown in the subject’s eyes Visual and Auditory Cortex Cortical Localization • Frontal Lobes – involved in speaking and muscle movements and in making plans and judgments • Parietal Lobes – include the sensory cortex The Cerebral Cortex The Cerebral Cortex • Motor Cortex – area at the rear of the frontal lobes that controls voluntary movements • Sensory Cortex – area at the front of the parietal lobes that registers and processes body sensations Association Areas • Areas of the cerebral cortex that are not involved in primary motor or sensory functions • Involved in higher mental functions such as learning, remembering, thinking, and speaking Cerebral Cortex Speech • Aphasia – impairment of language, usually caused by left hemisphere damage either to Broca’s area (impairing speaking) or to Wernicke’s area (impairing understanding) • Broca’s Area – an area of the frontal lobe that directs the muscle movements involved in speech • Wernicke’s Area – an area of the left temporal lobe involved in language comprehension and expression Specialization and Integration Brain Activity when Hearing, Seeing & Speaking Words Cortical Lateralization: Right and Left Hemispheres Function Differently • Right hemisphere: superior to the left hemisphere in visual and spatial tasks, recognizing nonlinguistic sounds, identifying faces, and perceiving and expressing emotions • Left hemisphere: superior to the right hemisphere at language, logic, and providing explanations for events • Women may be more likely than men to use both hemispheres for language (their brains are more bilateralized). Left-Handers are Different • 65% have speech on the left (95 % RH) • Weak correlations: – + gifted & creative – - reading disabilities, epilepsy, alcoholism, schizophrenia, allergies, MR Brain Reorganization • Corpus Callosum – large bundle of neural fibers connecting the two brain hemispheres and carrying messages between the hemispheres Brain Reorganization Corpus Callosum Brain Reorganization – Split Brain – a condition in which the two hemispheres of the brain are isolated by cutting the connecting fibers (mainly those of the corpus callosum) between them Brain Reorganization • The information highway from the eyes to the brain Testing the Split Brain The Brain Can Alter Its Neural Connections – Plasticity: the flexibility of the brain to alter its neural connections following injury – Hemispherectomy: a radical surgical procedure in which one of the cerebral hemispheres is removed to control life-threatening epileptic seizures. The remaining healthy hemisphere takes over many of the functions of the removed hemisphere. – Plasticity is highest in childhood, but it also occurs in older adults. Brain Reorganization -- the brain’s capacity for modification as evident in brain reorganization following damage (functional plasticity) --and in experiments on the effects of experience on brain development Structural Plasticity) Use it or Lose It • • • • • 1. 2. 3. 4. 5. Avoid Harmful Substances Exercise Eat Sensibly Challenge Yourself Mentally Wear Your Helmet/Seat Belt. Blood-Brain Barrier • A semipermeable wall of tiny blood vessels that prevent certain chemicals in the bloodstream from reaching the brain - Protects the brain from many “foreign substances” in the blood that may injure the brain, Protects the brain from hormones and neurotransmitters in the rest of the body, and Maintains a constant environment for the brain. Blood-Brain Barrier – Beneficial substances allowed to enter the brain through the blood-brain barrier are blood gases, such as oxygen, and small nutritional molecules. – An important nutritional molecule transported out of the bloodstream in this way is glucose. – Scientists have learned how to trick the bloodbrain barrier into accepting therapeutic drugs through the bloodstream to the brain. Blood-Brain BarrierBa