Neuro

• Limbic System


  An interconnected set of brain structures important for emotion, motivation, memory, and autonomic control

  
• Limbic "System"


  • A "system" in this case is loosely defined
• Limbic structures (Telencephalon)


  • Cingulate cortex
  • Insular cortex
  • Nucleus accumbens
  • Septal nuclei
  • Prefrontal cortex
  • Hippocampus
  • Amygdala
  • Olfactory system

  
• Limbic structures (Diencephalon)


  • Mammillary bodies in the hypothalamus
  • Anterior nucleus of the thalamus
  • Mammillothalamic tract
  • Fornix tract (output of the hippocampus)

  
• The hippocampus sends axons out via the fornix, and fornix fibers wrap around the diencephalon and terminate in the mammillary bodies

  
• Mammillary bodies project to the anterior thalamus, which projects to the cingulate gyrus
• Functional roles of the limbic system

  • Motivation and emotion – fear, anger
  • Self control
  • Learning and memory
  • Dysfunction contributes to psychiatric disease – addiction, mood disorders, schizophrenia
• Septal nuclei and nucleus accumbens

  Process motivation and reward, stimulation is "rewarding" or reinforcing
• Septal lesions


  Enhance aggression -> "septal rage"
• Prefrontal cortex


  Broad roles in executive function: complex cognition, abstraction, planning, and decision making, social awareness
• Selective damage to prefrontal cortex can decrease aggression
• Prefrontal lobotomy psychosis patients


  • Broader cognitive effects on intelligence
• Phineas Gage


  Railroad foreman with extensive damage to prefrontal cortex and anterior cingulate gyrus, became short tempered, impulsive, socially awkward
• Gage lived 12 more years and eventually recovered relatively normal function
• Damage to the medial temporal lobe


  Disrupts memory formation
• Patient H.M.


  • Treated for temporal lobe epilepsy with a bilateral lesion, unable to form new declarative memories but procedural memories were intact
• Korsakoff syndrome


  Damage to the mammillary bodies and thalamus, disruption in the ability to form new declarative memories, confabulation, apathy
• Papez circuit


  Hippocampus -> fornix tract -> mammillary bodies -> mammillothalamic tract -> anterior thalamus -> cingulate gyrus -> hippocampus, critical for declarative memory formation

  
• Amygdala


  Stimulation can evoke fear responses, elevated activity associated with fear and anxiety, damage reduces fear/threat responses
• Kluver-Bucy syndrome


  • Temporal lobe lesions, docility, low fear, unresponsive to threats, hypersexuality, compulsive eating
• Urbach-Wiethe disease


  • Bilateral loss of amygdala, low/no fear
• Fear can be induced in people with amygdala damage under the right conditions, suggesting "fear" is not fully localized in the amygdala
• Rewarding stimuli


  Stimulate dopamine release in the nucleus accumbens, needed for learning and motivational drive
• Cerebral Cortex


  Develops from the embryonic telencephalon
• Drugs of abuse exploit the endogenous reward system, producing exaggerated dopamine release in the nucleus accumbens
• Human cortex is estimated to contain 15 billion neurons
• Cerebral cortex


  Phylogenetically new, unlike the reticular formation from the previous lecture
• The size and complexity of the cortex is one of the defining features that differentiates humans from lower mammals

  
• Neocortex


  Most of the human cerebral cortex, has six layers

  
• Allocortex


  Has less than six layers, includes piriform cortex, olfactory tubercle, anterior olfactory nucleus, hippocampus, olfactory bulb, some others
• More layers are thought to reflect more complex processing
• Pyramidal neurons


  • Large, long dendrites, primary source of axons that leave the cortex
• Granule cells


  • Small and star-shaped, no apical dendrites
• Layers of the cortex

  • Layer I - Molecular Layer (most superficial)
  • Layer II - External Granule Cell Layer
  • Layer III - External Pyramidal Cell Layer
  • Layer IV - Internal Granule Cell Layer
  • Layer V - Internal Pyramidal Cell Layer
  • Layer VI - Multiform Layer (most internal)

  
• Layer I - Molecular Layer


  Contains mainly axons and dendrites from deeper layers, horizontal cells are the only cell type in this layer
• Layer II - External Granule Cell Layer

  Contains primarily granule cells, receives input from primarily other cortical areas
• Layer III - External Pyramidal Cell Layer

  Contains primarily pyramidal cells, sends axons primarily to other cortical areas
• Layer IV - Internal Granule Cell Layer

  Composed of primarily granule cells, receives afferent input primarily from the thalamus
• Layer V - Internal Pyramidal Cell Layer

  Composed primarily of large pyramidal cells with a large, apical dendrite, sends efferent output to subcortical regions

  
• Layer VI - Multiform Layer


  Contains a variety of cell types, less well understood, may receive input from and output to the thalamus