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S.M. and the amygdala

• Patient S.M. has Urbach-Wiethe disease, a rare autosomal recessive condition.
• It produces bilateral calcification and atrophy of the amygdala.
• Deficits observed in fear: S.M. struggles with fear comprehension and fear production on tasks.
• S.M. demonstrates a fear deficit on both recognition and production tasks, indicating a critical role of the amygdala in fear processing.
• The slide references Ekman’s work on universal emotional expressions, illustrating cross-cultural recognition of basic emotions (The universal emotional expressions by Paul Ekman).
• Overall implication: amygdala damage can severely disrupt fear processing while other emotions may remain intact.

The universal emotional expressions (Ekman)

• Paul Ekman’s research identifying universal facial expressions across cultures.
• These expressions are reliably recognized across diverse populations, suggesting innate, biologically based emotional signals.

The nervous system: Communication in the Nervous System

• Two major cell types: glia and neurons.
• Glia: supportive cells found throughout the nervous system.
  • Functions include:
  • Supply nourishment to neurons
  • Help remove waste products from neurons
  • Provide insulation around many axons
  • May send and receive chemical signals
  • Likely play roles in various major disorders
• Neurons: the primary information-processing cells that receive, integrate, and transmit information.

Neurons: Structure

• Soma: the cell body containing the nucleus and essential machinery.
• Dendrite: branched extensions specialized for receiving information.
• Axon: a long, thin fiber that transmits signals away from the soma to other neurons or to muscles/glands.

Myelin sheath, Nodes of Ranvier, and Terminal Button

• Myelin sheath: insulating fatty layer around some axons; speeds signal transmission.
• Nodes of Ranvier: gaps in the myelin sheath that facilitate rapid conduction via saltatory conduction.
• Terminal button: small knobs at axon ends; secrete neurotransmitters into the synapse.
• Synapse: region where a neuron transfers information to another cell.

The Synapse: Where Neurons Meet

• Synaptic cleft: the microscopic gap between the terminal button of one neuron and the membrane of another.
• Presynaptic neuron: the neuron that sends the signal across the synaptic gap.
• Postsynaptic neuron: the neuron that receives the signal.

Receptors and Neurotransmitters

• Receptor: a protein on the cell surface where neurotransmitters attach.
• Neurotransmitter: chemical messengers of the nervous system.

The Neural Impulse

• Resting potential: the stable, negative charge when the neuron is inactive.
• Action potential: a brief shift in the neuron’s electrical charge that travels along the axon when the neuron is stimulated.
• Conceptual layout (simplified): a change in net charge propagates along the axon to transmit information.

The Synapse: Presynaptic and Postsynaptic Roles

• Presynaptic neuron releases neurotransmitters into the synaptic cleft.
• Postsynaptic neuron contains receptors that respond to the neurotransmitters.

Resting Potential and Action Potential (electrical signaling within a neuron)

• Neuronal signaling is primarily electrochemical: electrical events inside neurons and chemical events at synapses.
• Action potential initiation leads to release of neurotransmitters, which then initiate communication between neurons.

Synapse: Reuptake and SSRIs

• Most neurotransmitters are reabsorbed into the presynaptic neuron through reuptake (reabsorbed from the synaptic cleft by the presynaptic membrane).
• SSRIs: selective serotonin reuptake inhibitors, a class of drugs that block reuptake to increase serotonin availability.

Electrical-to-Chemical-to-Electrical

• Neural communication is an electrochemical process:
  • Electrical: action potential travels within a neuron.
  • Chemical: neurotransmitter release at the synapse.
  • Electrical: postsynaptic response (post-synaptic potential) propagates as another electrical signal in the next neuron.

Postsynaptic Potentials (PSPs)

• Excitatory PSP (EPSP): positive voltage shift that increases the likelihood that the postsynaptic neuron will fire an action potential.
• Inhibitory PSP (IPSP): negative voltage shift that decreases the likelihood of firing.
• A neuron receives signals from thousands of other neurons and must integrate excitatory and inhibitory inputs before deciding whether to fire an action potential.

Video Demonstration

• Video demonstration: https://www.youtube.com/watch?v=hGDvvUNU-cw

Neurotransmitters: Chemical Messengers

• Different neurons release different neurotransmitters with diverse functions.
• Examples:
  • Glutamate: the primary excitatory neurotransmitter; most abundant in the brain.
  • GABA: the major inhibitory neurotransmitter in the brain.
  • Acetylcholine: regulates voluntary movement; muscle contraction; cognitive functions.
  • Dopamine: involved in movement, cognitive functions, reward pathways, and more.
  • Norepinephrine: involved in fight-or-flight responses; increases heart rate; arousal; cognition; mood; and more.

Neuroimaging: Techniques to Visualize the Brain

• Computerized Tomography (CT) scan
• Positron Emission Tomography (PET) scan
• Magnetic Resonance Imaging (MRI)
• Functional Magnetic Resonance Imaging (fMRI)

Brain Changes with Methamphetamine Use

• Methamphetamine use is associated with smaller brain mass and extensive brain tissue loss.
• Frontal lobes are among the most affected regions, leading to:
  • Apathy
  • Disinhibition
  • Diminished executive functioning
  • Impairments in formulating strategies and in decision making
• Average differences in brain tissue volume (meth users vs non-users):
  • $3\%\text{ loss}$
  • $5\%\text{ loss}$
• Areas of greatest loss include:
  • Emotion and reward systems (limbic system)
  • Memory (hippocampus)
• Dr. Paul Thompson (U.C.L.A.) described the study as showing a "forest fire of brain damage" and noted that more tissue loss was observed than expected.