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: • The case study method looks at the effects of brain damage due to stroke, head trauma, or other injury in humans. • 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 used to measure which brain areas are most active.
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 over time.
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.
Visual agnosias • A visual agnosia is an inability to recognize a visual object. There are two categories: • Apperceptive agnosia. Difficulty in assembling the pieces or features of an object together into a meaningful whole. • Associative agnosia. Can perceive a whole object but have difficulty naming or assigning a label to it.
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.
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.
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.
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: • Lowest level governs automatic responses. Location: posterior brain areas. • Intermediate supervisory level runs executive processes and solves problems. Location: frontal lobe. • Highest level is metacognitive. It monitors and regulates any aspect of cognition. Location: prefrontal cortex.