The Brain

Some interesting brain facts §Brain weighs 3 lbs l However, it is completely immersed in liquid (cerebrospinal fluid) and, as a result, its effective weight is 3 ounces. §Brain uses 20% of the body’s blood, 20% of its oxygen, and 70% of its glucose. §80% of the human brain is cortex l Cortex is virtually absent in fish, reptiles, and birds l 1/3 of the cortex is visible l Cortex is 1/8” thick and, if spread out flat, is about the size of 1 sheet of newspaper (4 pages of a textbook) §Localization of function vs. equipotentiality (mass action) l Broca’s area is in the frontal lobe; when destroyed, patient cannot produce language, but can comprehend language; Broca’s aphasia l Wernicke’s area is in the temporal lobe; when destroyed patient cannot comprehend language, but can produce language; Wernicke’s aphasia

Direction in the brain §We are symmetrical around our midline: we have a left arm and a right arm, a left ear and a right ear, etc. §Medial: close to the midline §Lateral: farther from the midline; closer to the “side” of the head

Some brain structure terminology §Sulcus (pl. sulci): any of the shallow grooves separating the convolutions (bumps, ridges) on the surface of the brain §Fissure: a very deep groove that, typically, separates major cortical structures §Gyrus (pl. gyri): a convolution (bump, ridge) on the brain surface §Commisures: a fiber bundle that interconnects corresponding regions on each side of the brain §White matter (mylinated axons) and gray matter (cell bodies) §Cortical structures are specialized parts of the cortex. l Everything else under the cortex, but above the brainstem, is referred to as a subcortical structure.

Some brain organization terminology §Hemispheres l The two relatively symmetrical halves of the brain; one on the left and one on the right §Contralaterality l The left hemisphere receives sensory input from, and sends motor messages to, the right side of the body; vice versa for the right hemisphere §Cerebral lateralization (hemispheric specialization) l Instances in which one of the hemispheres is more responsible for a particular cognitive function than the other hemisphere Left hemisphere specialized for language and analytical thought Right hemisphere specialized for visual-spatial tasks, music, face recognition, and emotional states §Cerebral dominance l In 90% of human beings, the left hemisphere is specialized for language and these individuals are right-handed; thus, the left hemisphere is said to be the dominant hemisphere

Brainstem §Medulla l Vital involuntary functions §Pons l Sleep and arousal §Reticular formation l Sleep, arousal, attention §Cerebellum l Motor coordination l Also involved in planning, memory, language, and emotion

Another view of the brainstem

Limbic System I: Emotion and motivation §Hypothalamus l Regulates Glands Autonomic system Eating Drinking Sleeping Sexual activity l Plays a role in emotion §Amygdala l Forms learned associations between objects and emotion, especially fear

Limbic system II: Cognitive functions §Thalamus l Sensory relay station §Hippocampus l Formation of new memories §Basal ganglia l Putamen, globus pallidus, caudate nucleus l Motor behavior l Habit learning

Another view of both the limbic system and brain stem

Neglect Syndrome (Hemineglect) §A patient with a stroke in the right hemisphere was asked to copy the model drawings §Typical of neglect syndromes, the left side of the model is almost completely ignored

Primary motor cortex and somatosensory cortex

The Nervous System

The Autonomic Nervous System “Fight or Flight”Restore Calm

The Endocrine System §Endocrine system: Ductless glands that regulate growth, reproduction, metabolism, mood, and some behavior §Hormones: chemical messengers secreted into the bloodstream §Chain of command l Hypothalamus commands the pituitary, which in turn releases hormones that command the other glands to release their hormones

Brain Change §Plasticity l A property of the brain that allows it to change as a result of experience, drugs, or injury §Chemical signals guide growing connections. §Experience fine-tunes neural connections. l Critical periods l Rats in special environments have heavier brains with more synaptic connections §Change in the strength of connections underlies learning l Hebbian learning: “fire together, wire together” §Neurogenesis: production of new brain cells in the adult brain §Brain reorganization in response to overuse or underuse l Devoting more cortex to information that is pertinent for tasks at hand Blind people who read Braille have much larger areas of cortex devoted to receiving input from index fingers than do sighted individuals §Brain reorganization in response to brain injury l Much more likely to occur in the young §Treatment for brain injury or disease l Neural grafting, using stem cells