brain

Sources:

• wikipedia
• GPT-4
• https://ocw.mit.edu/courses/9-13-the-human-brain-spring-2019/video_galleries/lecture-videos/

Major parts of the brain:

• forebrain (prosencephalon) contains
  • cerebrum (telencephalon) is the largest, outer/upper part, split into left and right hemispheres
    • cortex
    • basal ganglia
      • striatum (incl nucleus accumbens)
      • subthalamic nucleus
      • globus pallidus
      • substantia nigra
  • diencephalon (also classified as part of the brain stem) contains
    • thalamus: relay and filter for sensory and motor information passing to the cortex. can amplify or suppress sensory information, and is a clearinghouse for sensory information to come together. but it can't be the final 'binding' site in the sense of the binding problem because it doesn't see olfaction (which connects directly to the cortex).
      • filtering can be top-down controlled by feedback loops from the cortex
      • shuts down most sensory input during sleep
      • is the primary pathway for vision, auditory, somatic information to reach the cortex
    • hypothalamus (including posterior part of the pituitary): involved in maintaining homeostasis and hormone regulation. Mostly unconscious/involuntary functions, processing information from the autonomic nervous system: temperature regulation, appetite and thirst, circadian rhythm, sexual arousal, stress response. 'hypo' means 'under', so this is 'under the thalamus' (just like a hypodermic needle goes under the skin). about the size of a pearl.
    • epithalamus (includes pineal gland, which secretes melatonin)
• midbrain (mesencephalon): by far the smallest
• hindbrain (rhombencephalon)
  • cerebellum is attached to the back of the brain stem. related to fine motor control and coordination?
    • can still move without it, but not 'automatically' - every motion must be thought through laboriously
    • also relates to learned movements ('muscle memory'). essentially coordination is learned movement, since we don't have the bandwidth to consciously direct a sophisticated coordinated movement.
    • is also activated when thinking about moving even while still
    • may relate to predicting the results of muscle movements
    • !!! is apparently the seat of classical conditioning: the part of the brain that learns associations!
    • has gotten bigger in hominids since Neanderthals and even Cro-Magnon man, so is clearly important for higher thought.
  • pons
  • medulla oblongata

gray vs white matter: white matter is myelinated (covered with sheath of fatty myelin, which means faster signaling, but bulkier (lower computational density) and more energy expensive

amygdala: involved in emotional processing. anchor of the limbic system.

• three subparts:
  • medial nuclei connect to the olfactory bulb and olfactory cortex
  • basolateral nuclei: connects to the cerebral cortex, can receive highly processed sensory information
  • central and anterior nuclei: connect to the brainsteam and hypothalamus
• shown to be the basis of conditioned fear responses. if you train rats to be afraid of a tone that signals electric shock, then lesion the amygdala, they are not longer afraid of the tone.
• right hemisphere is involved in emotional control of speech: modulating the voice to sound angry or cheerful, etc.
• left hemisphere seems to be more positive emotions, right more negative?

memory:

• declarative memory (conscious awareness of facts) vs nondeclarative / procedural memory
• time durations:
  • 'immediate memory': the current conscious moment. eg, our view of the visual field is really a memory of recent saccades, but the brain assembles this into a coherent picture
  • 'short term memory': lasts seconds to minutes. debatably, just a form of attention to internal representations rather than sense data.
  • 'long term memory': physically embodied by changes in synaptic connections ('weights' more than 'activations')
• the hippocampus seems to be associated with long-term declarative memory formation. it is not itself the storage location --- the memories seem to be stored in the cortex --- so lesioning the hippocampus means that people retain their memories but can't form new ones.
• it seems that memories are stored to some extent 'locally' in the cortex. so visual memories are stored in visual cortices, auditory memories in auditory cortices, etc.
• nondeclarative memory formation seems to rely on the premotor cortex, basal ganglia, and cerebellum.