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Functional Neural Anatomy Honors Psychology Linking Structure & Function • Three Types of Evidence • Association of function: “If brain area A controls behavior X, then those with deficient behavior X will have a deficient area A, and individuals with a better behavior X will have a better area A.” • Single dissociation of function: “If brain area A controls behavior X, then those with a deficient area A will have a deficient behavior X but not Y ….” • Double dissociation of function: “If brain area A controls behavior X, then those with a deficient area A will have a deficient behavior X but not Y, and those with a deficient area B will have a deficient behavior Y but not X ….” Tools of Functional Anatomy Situation #1: When you can kill the animal • • Analysis of structure • • Ablations: the removal of a brain area Lesions: the destruction of brain areas, e.g., accidental lesions, or as a result of the deliberate application of electrodes, chemicals, or gene-knockouts. Analysis of activity • Microdialysis: a method for measuring concentrations of neurotransmitters Tools of Functional Anatomy Situation #2: When you can’t • • Analysis of structure • • CAT scans provide a high-contrast x-ray of the brain with excellent spatial resolution, but provide no temporal resolution MRIs provide higher resolution images of the brain and use no radiation, but provide no temporal resolution. Analysis of activity • • • EEGs record electrical activity of the brain through electrodes attached to the scalp, thereby providing excellent temporal records of neural processes but poor spatial resolution. PET scans provide a high-resolution image of brain activity with moderate temporal and spatial resolution. fMRIs have excellent spatial resolution and near-excellent temporal resolution. The Basics of the Nervous System • • Three basic functions: • • • To receive sensory information To organize and integrate that information with past information To enact the muscles and glands to produce organized movements and adaptive secretions Three basic structures: • • • Sensory neurons Interneurons Motor neurons Nervous System Hierarchy • Animal evolution involved moving from simple reflexes to intentional control of movement. • This evolution is (roughly) manifest in the hierarchical organization of motor control. • • At the simplest level, motor neurons work alone to control muscles. At higher levels, muscles are controlled by motor neurons, which are controlled by the brainstem, which is controlled by the primary motor cortex, which is controlled by the.... Central vs. Peripheral Central Nervous System: • • Brain Cortical Structures Subcortical Structures Spinal Cord • • Peripheral Nervous System: • • Nerves connecting the CNS with organs and muscles Autonomic Nervous System Sympathetic ganglia Parasympathetic ganglia • • Central Nervous System Peripheral Nervous System Autonomic Nervous System Sympathetic Division--the war-maker preparing for “fight or flight” • Primarily, the function of these neural cell bodies (or ganglia) is • • • to accelerate breathing and heart rate and to decrease digestive activity to preserve energy for the muscles Activated secondarily (or “in sympathy”) are • • • • the sweat glands, adrenal glands, the muscles that constrict blood vessels, and the muscles that make your hair stand on end. Autonomic Nervous System • Parasympathetic Division--the peace-keeper that heals, promotes growth, conserves energy • • Parasympathetic ganglia are not linked to one another as tightly as the sympathetic Consequently, they • • • increase the digestive rate, decrease the heart rate, increase the flow of sinus fluids independently Spinal Cord • Sends and receives input from the sense organs and muscles below the level of the head • • • Bell-Magendie Law: entering dorsal roots carry sensory information to the brainstem and exiting ventral roots carry motor information to the muscles and glands. Contains networks of neurons, pattern generators, that stimulate one another cyclically to generate rhythmic sequences of motor movements, such as flying, walking, running, etc. The brain inhibits these movements. Subserves some reflexes, such as the flexion reflex, which removes a limb from a potentially damaging reflex even without the perception of pain. Subcortical Structures/Brainstem Subcortical Structures/Brainstem Subcortical Structures/Brainstem Subcortical Structures/Brainstem • The Brainstem • • • Medulla controls vital reflexes such as breathing, heart rate, and vomiting, and exerts control over the spinal cord. During REM sleep, for example, the medulla is activated and suppresses movement. Pons receives input from facial skin, nose, mouth, eye muscles, and part of the tongue. It also controls chewing and swallowing, eye movements, and facial expressions. Midbrain controls the speed of locomotion and with the pons controls levels of arousal. In birds, reptiles, amphibians, and fish the midbrain is proportionately larger than in mammals. When a mammal’s midbrain is cut, it can react to stimuli (such as to climb a pole whether or not it has food at the top) but it cannot selectively react to stimuli (such as to climb a pole that has food at the top rather than a pole that does not). Subcortical Structures/Thalamus Subcortical Structures/Thalamus • The thalamus is a sort of relay station. • • Non-olfactory sensory information goes first to the thalamus, which then processes it and relays the output to the cerberal cortex. Relays information in modality-specific ways. • • • Many nuclei in the thalamus receive their input primarily from the visual system, then relays the information to a single area of the cerebral cortex, while receiving feedback information from the same cortical area. The thalamus also relays information from higher parts of the brain to movementcontrol centers in the brainstem. Lesions placed in some thalamic nuclei can temporarily relieve the deep, chronic pain caused by chemotherapy without abolishing the patient’s physical sensations. Subcortical Structures/Cerebellum • The cerebellum responds to sensory information that guides movements that require the rapid integration of sensory information, such as flying and tree hopping. • • Birds and monkeys, for example, have particularly large cerebella. Cerebellar lesions in sloths had no detectable effect. People with damage to the cerebellum look drunk, and • • • have trouble moving their eyes to a particular point have trouble shifting their attention from visual to auditory information have trouble tapping a rhythm, pointing at a moving object, and adapting to prisms that distort vision Subcortical Structures/Limbic System • • The limbic system forms a border around the thalamus and basal ganglia. The limbic system includes • • • hypothalamus, hippocampus, amygdala. Subcortical Structures/Limbic System • In rabbits, cats, and monkeys, it takes up a large proportion of the brain. Subcortical Structures/Limbic System • • • The primary tasks of the hypothalamus: • • • to influence the activity of the autonomic nervous system, control the release of certain hormones, influence hunger and thirst. • When the amygdala is removed or diseased, people are not startled by loud sounds, experience fear very weakly, and have difficulty recognizing fear in others. The amygdala seems to be responsible for emotional learning. The hippocampus serves spatial memory in non-humans, and serves to convert short-term to long-term memories in humans. Subcortical Structures/Basal Ganglia • The basal ganglia exchanges information with the cerebral cortex, itself, and the thalamus. • • • The function of the basal ganglia seems to be to organize movement plans from the cerebral cortex by inhibiting unwanted movements. As a result, it is important for slow, deliberate movements, such as a reaching for an object. One study of very clumsy children found that those with cerebellar impairment were inaccurate with the timing of their movements, whereas those with basal ganglia impairments were inaccurate in their control of muscle force (Lundy-Ekman, et al., 1991). The basal ganglia may also be important for inhibiting unwanted thoughts. Psychotherapy and drug-treatments of obsessive-compulsive disorder seem to work by lowering the metabolic rate of the basal ganglia. Nervous System: Phylogeny • • • Species-differences involve differences in “smoothness” and differences in the amount of cortex relative to the body, which is related to species-typical diets (e.g., fruit-eating bats have relatively bigger brains than insect-eating bats; carnivores have relatively bigger brains than herbivores) and basal metabolic rate. Primates devote more energy to brain development than any other species. Other species-differences relate to specific areas of the brain, such as the olfactory lobe (smell), hippocampus (spatial abilities), Nervous System: Ontogeny • • The development of the cortex shows a roughly similar pattern as the phylogenetic differences: relatively small and smooth cortex early in development. This observation was expressed by 19th century biologists as “ontogeny recapitualates phylogeny.” Cortex Evolution: Does size matter? Cortex Evolution: Does size matter? Cortex Evolution: Does size matter? Cortex Evolution: Apes vs. Humans • Motor and visual areas are proportionately smaller in humans (77% & 60%), whereas the prefrontal area is 202% larger. Cortex Evolution: Apes vs. Humans • • • The human brain has more axons between cortical areas and between the basal ganglia. Humans control their vocalizations primarily from the cortex rather than the limbic system. Some neurotransmitters are proportionately more widespread in humans than in apes. The Truth about Cortex • The Truth about the brain – What is true: People get sensory information, think about it, and act. – What is not: “Sensory area” gets sensory information; “association area” thinks about it; “motor area” acts on it. • Why? – Association cortex processes information more elaborately than the primary sensory areas do, but they do not link one kind of sensory information with another. Only visual info goes to associative visual cortex; only auditory info goes to associative auditory cortex, etc. – The brain has no single site at which all information funnels into a hidden observer. There is no “little person in the brain.” – Thinking depends on separate, simultaneous processes throughout the brain. How they produce a unified consciousness remains a mystery. • Consequently, we divide the brain into lobes named for the skull bones which cover them. Cerebral Cortex • The occipital lobe primarily receives information about objects that we see. • Destruction of the top layer causes cortical blindness: normal eyes, normal pupillary reflexes, some eye movements, but no pattern perception. Cerebral Cortex • The parietal lobe primarily receives information from the pressure that we feel by touch. • Destruction of parietal cortex does not lead to total loss of the sense of touch, but rather difficulties in using such information. For example, blind people lose the ability to read Braille. Other symptoms include: clumsiness on the side of the body opposite the damage, the inability to draw and follow maps, and the inability to say what something might look like when viewed from a different angle. Cerebral Cortex • The temporal lobe primarily receives information from the tones that we hear. • Damage to the temporal lobe affects the ability to understand both spoken and signed language. Cerebral Cortex • The frontal lobe contains the motor and prefrontal cortex. • • The primary motor cortex is necessary for making delicate hand movements, such as lifting a small piece of food out of a narrow hole. The supplementary motor cortex is necessary for visualizing motor sequences such as visualizing a basketball shot you’re about to make. More complex tasks require greater activation of this area. The amazing prefrontal cortex • • The prefrontal cortex is the only cortical area that receives information from all the sensory systems, including the interior of the body. The prefrontal cortex is important for • • • working memory, the ability to remember recent events, such as how many people ran in vs. out of a building delayed response tasks, in which a stimulus appears, then disappears, and after a delay, the person must respond to the remembered stimulus monitoring recent events, calculating possible actions, ascertaining the results of those actions, and determining the emotional value of each of those outcomes. Damage to your PFC may result in showering with your clothes on, shaking salt into your drink instead of your food, or pouring water on the tube of toothpaste rather than your toothbrush.