Chapter SixChapter Six

The Neuroscience Approach: The Neuroscience Approach: Mind As BrainMind As Brain

NeuroscienceNeuroscience

• The study of nervous system anatomy and The study of nervous system anatomy and physiology in man and other species.physiology in man and other species.

• Cognitive neuroscienceCognitive neuroscience studies the studies the structures and processes underlying structures and processes underlying cognitive function.cognitive function.

• What are the neural mechanisms for pattern What are the neural mechanisms for pattern recognition, attention, memory, and problem recognition, attention, memory, and problem solving?solving?

Neuroscience methodsNeuroscience methods

In brain damage techniques investigators study the In brain damage techniques investigators study the effects of accidental or deliberate nervous- effects of accidental or deliberate nervous- system damage. There are two types:system damage. There are two types:

1.1. The The case study methodcase study method looks at the effects of looks at the effects of brain damage due to stroke, head trauma, or brain damage due to stroke, head trauma, or other injury in humans.other injury in humans.

2.2. In In lesion studieslesion studies, an electrode is used to , an electrode is used to selectively destroy a specific brain area of an selectively destroy a specific brain area of an animal. The resulting behavioral deficits are then animal. The resulting behavioral deficits are then examined.examined.

Brain recording techniquesBrain recording techniques

• The brain’s electrical activity can be The brain’s electrical activity can be measured in a variety of ways.measured in a variety of ways.

• In In single-cell recordingsingle-cell recording an electrode is an electrode is inserted into or adjacent to a neuron.inserted into or adjacent to a neuron.

• In In multiple-unit recordingmultiple-unit recording, a larger electrode , a larger electrode is used to measure the activity of a group of is used to measure the activity of a group of neurons.neurons.

Brain recording techniquesBrain recording techniques

• An An electroencephalogramelectroencephalogram (EEG) provides (EEG) provides an even broader view of brain action. an even broader view of brain action. Electrodes placed on the scalp measure the Electrodes placed on the scalp measure the gross electrical activity of the entire brain.gross electrical activity of the entire brain.

• An EEG recording in response to the An EEG recording in response to the presentation of a stimulus is an presentation of a stimulus is an event-event-related potentialrelated potential..

Brain imagingBrain imaging

• Recent years have seen the introduction of more Recent years have seen the introduction of more sophisticated devices.sophisticated devices.

• Computer Axial TomographyComputer Axial Tomography (CAT). X-rays (CAT). X-rays passed through the brain from different passed through the brain from different perspectives are used to construct 2-D and 3-D perspectives are used to construct 2-D and 3-D images.images.

• Positron Emission TomographyPositron Emission Tomography (PET). (PET). Radioactively tagged glucose molecules used to Radioactively tagged glucose molecules used to measure which brain areas are most active.measure which brain areas are most active.

Brain imagingBrain imaging

• In In magnetic resonance imagingmagnetic resonance imaging (MRI) soft (MRI) soft tissue structure is measured by the tissue structure is measured by the alignment of protons within a powerful alignment of protons within a powerful magnet.magnet.

• Functional magnetic resonance imagingFunctional magnetic resonance imaging (fMRI) is a version that shows changes in (fMRI) is a version that shows changes in brain activity over time.brain activity over time.

Electrical stimulationElectrical stimulation

• In this procedure neurons are electrically In this procedure neurons are electrically stimulated and the resulting behavior is stimulated and the resulting behavior is studied.studied.

• Involves activation of brain areas rather than Involves activation of brain areas rather than their destruction or passive measurement.their destruction or passive measurement.

Anatomy of a neuronAnatomy of a neuron

Anatomy of a synapseAnatomy of a synapse

The cortexThe cortex

Visual pathwaysVisual pathways

Visual agnosiasVisual agnosias

• A visual agnosia is an inability to recognize A visual agnosia is an inability to recognize a visual object. There are two categories:a visual object. There are two categories:

1.1. Apperceptive agnosiaApperceptive agnosia. Difficulty in . Difficulty in assembling the pieces or features of an assembling the pieces or features of an object together into a meaningful whole.object together into a meaningful whole.

2.2. Associative agnosiaAssociative agnosia. Can perceive a whole . Can perceive a whole object but have difficulty naming or object but have difficulty naming or assigning a label to it.assigning a label to it.

ProsopagnosiaProsopagnosia

• Prosopagnosia is another type of agnosia in Prosopagnosia is another type of agnosia in which patients have difficulty recognizing which patients have difficulty recognizing faces.faces.

• In humans, cells that respond to faces are In humans, cells that respond to faces are found in the fusiform face area (FFA) found in the fusiform face area (FFA) located in the temporal lobe.located in the temporal lobe.

Neural models of attentionNeural models of attention

• In this In this component process modelcomponent process model of of attention, different brain areas perform attention, different brain areas perform distinct functions (Posner, et. al., 1987).distinct functions (Posner, et. al., 1987).

• Parietal lobe disengages attention from a Parietal lobe disengages attention from a fixed position.fixed position.

• Superior colliculus moves attention to a new Superior colliculus moves attention to a new location.location.

• Thalamus engages attention at the new Thalamus engages attention at the new position.position.

Neural models of attentionNeural models of attention

• In this In this distributed network modeldistributed network model (Mesulam, 1981) (Mesulam, 1981) the brain areas subsuming attention are redundant the brain areas subsuming attention are redundant and can perform multiple functions.and can perform multiple functions.

• Posterior parietal cortex provides a sensory map Posterior parietal cortex provides a sensory map of space to which attention is directed.of space to which attention is directed.

• Cingulate cortex determines what is important to Cingulate cortex determines what is important to pay attention to and what can be ignored.pay attention to and what can be ignored.

• Frontal cortex coordinates motor programs.Frontal cortex coordinates motor programs.• Reticular structures generate arousal and Reticular structures generate arousal and

vigilance levels.vigilance levels.

Neuroscience of memoryNeuroscience of memory

• Karl Lashley (1950) searched for the Karl Lashley (1950) searched for the engramengram, the physical location of a memory., the physical location of a memory.

• He destroyed progressively larger areas of He destroyed progressively larger areas of monkey brain tissue after training them on a monkey brain tissue after training them on a task.task.

• The monkeys retained the memory, The monkeys retained the memory, suggesting it was distributed to many parts suggesting it was distributed to many parts of the brain, a principle known as of the brain, a principle known as equipotentialityequipotentiality..

Learning and memoryLearning and memory

• LearningLearning is a change in the nervous system is a change in the nervous system caused by some event that in turn causes a caused by some event that in turn causes a change in behavior.change in behavior.

• Learning in a nervous system requires a change in Learning in a nervous system requires a change in the structure or biochemistry of a synapse, what is the structure or biochemistry of a synapse, what is called called synaptic plasticitysynaptic plasticity..

• If a group of neurons is repeatedly activated, the If a group of neurons is repeatedly activated, the synaptic connections between them will be synaptic connections between them will be strengthened. This circuit will then contain the new strengthened. This circuit will then contain the new information.information.

The hippocampusThe hippocampus

• This brain structure is responsible for This brain structure is responsible for consolidationconsolidation, the transfer of information from STM , the transfer of information from STM to LTM.to LTM.

• Damage to the hippocampus results in Damage to the hippocampus results in anterograde amnesiaanterograde amnesia, an inability to retain new , an inability to retain new information subsequent to the damage. Example: information subsequent to the damage. Example: The tragic case of H.M.The tragic case of H.M.

• This should be distinguished from This should be distinguished from retrograde retrograde amnesiaamnesia, in which it is difficult to remember , in which it is difficult to remember information learned prior to a traumatic incident.information learned prior to a traumatic incident.

Hippocampal structure and Hippocampal structure and functionfunction

Neural substrates of working Neural substrates of working memorymemory

• Storage of verbal material: posterior parietal Storage of verbal material: posterior parietal cortex in left hemisphere.cortex in left hemisphere.

• Rehearsal of verbal material: prefrontal Rehearsal of verbal material: prefrontal cortex.cortex.

• Storage of spatial information: posterior Storage of spatial information: posterior parietal cortex in right hemisphere.parietal cortex in right hemisphere.

• Maintenance of spatial information: Maintenance of spatial information: dorsolateral prefrontal cortex.dorsolateral prefrontal cortex.

Neural substrates of long-term Neural substrates of long-term memorymemory

• Semantic memory linked to the limbic Semantic memory linked to the limbic cortex.cortex.

• Consolidation of episodic memory mediated Consolidation of episodic memory mediated by the hippocampus.by the hippocampus.

• Procedural memory function associated with Procedural memory function associated with basal ganglia and motor cortex.basal ganglia and motor cortex.

Neuroscience of problem solvingNeuroscience of problem solving

• Patients with Patients with executive dysfunctionexecutive dysfunction have have difficulty starting and stopping behaviors and difficulty starting and stopping behaviors and in problem solving. They suffer frontal lobe in problem solving. They suffer frontal lobe damage.damage.

• They may also be impelled to engage in a They may also be impelled to engage in a behavior triggered by a stimulus. This is behavior triggered by a stimulus. This is called called environmental dependency environmental dependency syndromesyndrome. Example: seeing a pen causes . Example: seeing a pen causes them to pick it up and start writing. them to pick it up and start writing.

The Tower of London problemThe Tower of London problem Left anterior frontal lobe damage seems to Left anterior frontal lobe damage seems to

underlie planning and sequencing in this task underlie planning and sequencing in this task (Shallice, 1982).(Shallice, 1982).

Theories of executive functionTheories of executive function

• Executive functionExecutive function refers to the cognitive refers to the cognitive operations used in problem solving. They include operations used in problem solving. They include planning, sequencing of behavior, and goal planning, sequencing of behavior, and goal attainment.attainment.

• Automatic attentional processesAutomatic attentional processes do not require do not require conscious control. They are triggered by conscious control. They are triggered by environmental stimuli.environmental stimuli.

• Controlled attentional processesControlled attentional processes require conscious require conscious control. Made in response to novel or difficult control. Made in response to novel or difficult situations.situations.

Theories of executive functionTheories of executive function

• In the Norman-Shallice (1980) model, action In the Norman-Shallice (1980) model, action schemas are activated by stimuli or other schemas schemas are activated by stimuli or other schemas and produce a behavior. and produce a behavior.

• Action schemas are like scripts in that they specify Action schemas are like scripts in that they specify what to do in a specific situation. They control what to do in a specific situation. They control automatic attentional processes.automatic attentional processes.

• Action schemas inhibit one another so that Action schemas inhibit one another so that multiple actions are not executed simultaneously. multiple actions are not executed simultaneously. Called Called contention schedulingcontention scheduling..

• This system works well for routine familiar tasks.This system works well for routine familiar tasks.

Theories of executive functionTheories of executive function

• But for new or difficult problem solving situations But for new or difficult problem solving situations for which there is no known solution, another for which there is no known solution, another system is needed.system is needed.

• The The Supervisory Attentional SystemSupervisory Attentional System (SAS) has (SAS) has more general flexible strategies that can be more general flexible strategies that can be applied to any problem situation.applied to any problem situation.

• The SAS monitors schemas and can suppress or The SAS monitors schemas and can suppress or turn off inappropriate ones.turn off inappropriate ones.

• Probable neural location is the left anterior frontal Probable neural location is the left anterior frontal lobe.lobe.

Theories of executive functionTheories of executive function

• Stuss and Benson (1986) propose an Stuss and Benson (1986) propose an alternate model with three levels:alternate model with three levels:1.1. Lowest level governs automatic responses. Lowest level governs automatic responses.

Location: posterior brain areas.Location: posterior brain areas.2.2. Intermediate supervisory level runs executive Intermediate supervisory level runs executive

processes and solves problems. Location: processes and solves problems. Location: frontal lobe.frontal lobe.

3.3. Highest level is Highest level is metacognitivemetacognitive. It monitors and . It monitors and regulates any aspect of cognition. Location: regulates any aspect of cognition. Location: prefrontal cortex.prefrontal cortex.