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 (ERP).

Brain Imaging Methods  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 Methods  In magnetic resonance imaging (MRI) soft tissue structure is measured by the alignment of protons within a powerful magnet. A “snapshot”.  Functional magnetic resonance imaging (fMRI) is a version that shows changes in brain activity over time. A “movie”.

Brain Imaging Methods  Magnetoencephalography (MEG) measures changes in small magnetic fields that occur when neurons fire. Better spatial and temporal resolution than fMRI.  Knife-edge scanning microscope (KESM) takes pictures of slices of tissue and reconstructs a 3-D image.  A complete 3-D cellular-level recording of the human brain is now possible.

Electrical Stimulation Techniques  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.  In transcranial magnetic stimulation (TMS) an electrical current is passed through a part of the brain causing neurons to fire.  Repetitive applications can be used to treat psychological disorders.

Anatomy of a Neuron

Anatomy of a Synapse

Neurotransmitters

Directions in the Nervous System  Dorsal – “Top”.  Ventral – “Bottom”.  Anterior – “Front”.  Posterior – “Back”.  Medial – “Middle”.  Lateral – “Side”.

Major Cortical Features  Two cerebral hemispheres on each side, one on the left, the other on the right.  Corpus callosum connects each hemisphere.  A gyrus is a fold of cortical tissue.  A fissure is a cleft or separation between gyri.

The Cortex

Left-Brain Functions Analytic thought Logic Language Science and Math Right-Brain Functions Holistic thought Intuition Creativity Art and Music

The Split Brain  Information from one side of the environment or body is mapped onto the contralateral side.  In split brain patients, the corpus callosum is severed  It is now possible to present information to only one side or the other – with interesting results.

Visual Pathways

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. 2. 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.

Disorders of Attention  Damage to the right superior temporal gyrus causes hemispatial neglect, an inability to attend to the left side of the body and the environment.  These patients can only perceive the right side of objects and will leave out the left sides when asked to draw them.

Disorders of Attention  Attention deficit hyperactive disorder (ADHD) is characterized by distractibility, impulsivity, getting easily upset, and difficulty in planning or carrying out plans.  The gene for one type of dopamine receptor is more common in some patients who also have smaller brains.  Treated pharmacologically with Ritalin

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, a process called long-term potentiation (LTP). This circuit will then “contain” the new information or mediate the learned behavior.

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. The inability to stop an action once started is called psychological inertia. 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.

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.

Interdisciplinary Crossroads: Neural Synchrony  Each object is made up of many different features like shape, color, motion, etc.  Different parts of the brain process each of these features.  How do all of these features get combined together so that we can recognize them? This is the perceptual binding problem.  The neurons in each of the different areas start to fire at the same time.