Chapter Six

1. Chapter Six The Neuroscience Approach: Mind As Brain

2. 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?

3. 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.

4. 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.

5. 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.

6. 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).

7. 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.

8. 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.

9. Anatomy of a neuron

10. Anatomy of a synapse

11. The cortex

12. Visual pathways (motion & location) (color & form) See also, Image 722 from Gray’s Anatomy

13. 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. “General damage to the occipital lobes and nearby areas.” • 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”

14. 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.)

15. Alternative Theoryof 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

16. 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.

17. 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.

18. 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

19. 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

20. Stroop Effect Read the word: RED

21. 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.

22. 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.

23. 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.

24. Hippocampal structure and function Sensory information

25. 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.

26. 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.

27. 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.

28. The Tower of London problem • Left anterior frontal lobe damage seems to underlie planning and sequencing in this task (Shallice, 1982).

29. 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.

30. 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.

31. 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.

32. 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.