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Chapter Six The Neuroscience Approach: Mind As Brain Neuroscience • The study of nervous system anatomy and physiology in man and other species. • Cognitive neuroscience studies the structures and processes underlying cognitive function. • What are the neural mechanisms for pattern recognition, attention, memory, and problem solving? Neuroscience methods In brain damage techniques investigators study the effects of accidental or deliberate nervous- system damage. There are two types: 1. The case study method looks at the effects of brain damage due to stroke, head trauma, or other injury in humans. 2. In lesion studies, an electrode is used to selectively destroy a specific brain area of an animal. The resulting behavioral deficits are then examined. Brain recording techniques • The brain’s electrical activity can be measured in a variety of ways. • In single-cell recording an electrode is inserted into or adjacent to a neuron. • In multiple-unit recording, a larger electrode is used to measure the activity of a group of neurons. Brain recording techniques • An electroencephalogram (EEG) provides an even broader view of brain action. Electrodes placed on the scalp measure the gross electrical activity of the entire brain. • An EEG recording in response to the presentation of a stimulus is an event- related potential. Brain imaging • Recent years have seen the introduction of more sophisticated devices. • Computer Axial Tomography (CAT). X-rays passed through the brain from different perspectives are used to construct 2-D and 3-D images. • Positron Emission Tomography (PET). Radioactively tagged glucose molecules (in the blood stream) used to measure which brain areas are most active (and get most blood supply). Brain imaging • In magnetic resonance imaging (MRI) soft tissue structure is measured by the alignment of protons within a powerful magnet. • Functional magnetic resonance imaging (fMRI) is a version that shows changes in brain activity (blood flow and oxygen level) over time. Current method of choice for investigating brain function. Electrical stimulation • In this procedure neurons are electrically stimulated and the resulting behavior is studied. • Involves activation of brain areas rather than their destruction or passive measurement. Anatomy of a neuron Anatomy of a synapse The cortex Visual pathways (motion & location) (color & form) See also, Image 722 from Gray’s Anatomy Visual agnosias • A visual agnosia is an inability to recognize a visual object. There are two categories: 1. Apperceptive agnosia. Difficulty in assembling the pieces or features of an object together into a meaningful whole. “General damage to the occipital lobes and nearby areas.” 2. Associative agnosia. Can perceive a whole object but have difficulty naming or assigning a label to it. “Damage to the connections that enable the formation of object representations” Prosopagnosia • Prosopagnosia is another type of agnosia in which patients have difficulty recognizing faces. • In humans, cells that respond to faces are found in the fusiform face area (FFA) located in the temporal lobe. • (Based on fMRI studies.) Alternative Theory of the Two Visual Pathways The ventral pathway is For object recognition “Vision for perception” Leads to consciousness & awareness of object The dorsal pathway is For visuomotor control “Vision for action” Nonconscious, only “here and now” Consider blindsight. See Milner & Goodale, The Visual Brain in Action Neural models of attention • In this component process model of attention, different brain areas perform distinct functions (Posner, et. al., 1987). • Parietal lobe disengages attention from a fixed position. • Superior colliculus moves attention to a new location. • Thalamus engages attention at the new position. Neural models of attention • In this distributed network model (Mesulam, 1981) the brain areas subsuming attention are redundant and can perform multiple functions. • Posterior parietal cortex provides a sensory map of space to which attention is directed. • Cingulate cortex determines what is important to pay attention to and what can be ignored. • Frontal cortex coordinates motor programs. • Reticular structures generate arousal and vigilance levels. Attentional Structures (p. 183-4) Reticular Activating System (RAS) In midbrain Controls overall arousal and alertness level Superior Colliculus In midbrain Shifting of visual attention Thalamus Relay center and filter for further processing Attentional Structures (cont) Parietal Lobe Binding of visual features Allocation of attentional resources Cingulate Cortex Response selection to competing inputs See Stroop Effect Frontal Lobe Goal-directed action Executive and problem solving Stroop Effect Read the word: RED Neuroscience of memory • Karl Lashley (1950) searched for the engram, the physical location of a memory. • He destroyed progressively larger areas of monkey brain tissue after training them on a task. • The monkeys retained the memory, suggesting it was distributed to many parts of the brain, a principle known as equipotentiality. Learning and memory • Learning is a change in the nervous system caused by some event that in turn causes a change in behavior. • Learning in a nervous system requires a change in the structure or biochemistry of a synapse, what is called synaptic plasticity. • If a group of neurons is repeatedly activated, the synaptic connections between them will be strengthened. This circuit will then contain the new information. The hippocampus • This brain structure is responsible for consolidation, the transfer of information from STM to LTM. • Damage to the hippocampus results in anterograde amnesia, an inability to retain new information subsequent to the damage. Example: The tragic case of H.M. • This should be distinguished from retrograde amnesia, in which it is difficult to remember information learned prior to a traumatic incident. Hippocampal structure and function Neural substrates of working memory • Storage of verbal material: posterior parietal cortex in left hemisphere. • Rehearsal of verbal material: prefrontal cortex. • Storage of spatial information: posterior parietal cortex in right hemisphere. • Maintenance of spatial information: dorsolateral prefrontal cortex. Neural substrates of long-term memory • Semantic memory linked to the limbic cortex. • Consolidation of episodic memory mediated by the hippocampus. • Procedural memory function associated with basal ganglia and motor cortex. Neuroscience of problem solving • Patients with executive dysfunction have difficulty starting and stopping behaviors and in problem solving. They suffer frontal lobe damage. • They may also be impelled to engage in a behavior triggered by a stimulus. This is called environmental dependency syndrome. Example: seeing a pen causes them to pick it up and start writing. The Tower of London problem Left anterior frontal lobe damage seems to underlie planning and sequencing in this task (Shallice, 1982). Theories of executive function • Executive function refers to the cognitive operations used in problem solving. They include planning, sequencing of behavior, and goal attainment. • Automatic attentional processes do not require conscious control. They are triggered by environmental stimuli. • Controlled attentional processes require conscious control. Made in response to novel or difficult situations. Theories of executive function • In the Norman-Shallice (1980) model, action schemas are activated by stimuli or other schemas and produce a behavior. • Action schemas are like scripts in that they specify what to do in a specific situation. They control automatic attentional processes. • Action schemas inhibit one another so that multiple actions are not executed simultaneously. Called contention scheduling. • This system works well for routine familiar tasks. Theories of executive function • But for new or difficult problem solving situations for which there is no known solution, another system is needed. • The Supervisory Attentional System (SAS) has more general flexible strategies that can be applied to any problem situation. • The SAS monitors schemas and can suppress or turn off inappropriate ones. • Probable neural location is the left anterior frontal lobe. Theories of executive function • Stuss and Benson (1986) propose an alternate model with three levels: 1. Lowest level governs automatic responses. Location: posterior brain areas. 2. Intermediate supervisory level runs executive processes and solves problems. Location: frontal lobe. 3. Highest level is metacognitive. It monitors and regulates any aspect of cognition. Location: prefrontal cortex.
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