Brain

Evolution of the Brain

600m ya - Bilaterians and Steering

Valence

• Bilaterians are the only animals that have brains
• Nematodes (legless wormlike creatures about the size of a grain of rice) emerge in the Edicaran period from 635 to 539m ya.
• Brain had 302 neurons (against 85 billion today
• Initial steering is obtained through assessing the valence (goodness or badness) of a stimulus, and going towards the things that smelled good and away from the things that smelled bad.
• There were negative and positive valence sensing neurons and move forward neurons and turning neurons.
• The various sensory inputs acted as votes for going one way or another and the first brains evolved as a mega-integration place to take in all these votes and then decide who had won and thus where to steer.

Emotions

• Affect is the name for the unifying foundation of emotions
• In addition to valance (good or bad), there is arousal (high or low)
• A primitive good mood encourages feeding, digesting, and sexual activity
• A primitive bad mood inhibits these activities
• An aroused good mood leads to exploiting nearby food sources or sexual partners
• An aroused bad mood leads to escaping from bad feelings - hunger, fear
• The brain generates affective states using neuromodulators like dopanmine and serotonin.
• In the nematode, dopamine is released to create arousal and drive the search for food and serotonin is released to suppress arousal and drive the enjoyment of digesting it.
• Dopamine is less about liking things and more about wanting them.
• Other neuromodulators - norepinephrine, octopamine, and epinephrine drive escape behavior by suppressing the effectiveness of serotonin and stopping an animal from being able to rest and feel safe - acute stress response.
• Opioids initiate recovery processes and inhibit negative valence neurons to stop and recover from stress episodes.
• Chronic stress turns off arousal and motivation, activates serotonin and leads to numbness and depression (anhedonia). It can cause learned helplessness
• Affect answers two questions:
  • Do I want to expend energy by moving?
  • Do I want to stay here or leave?

Associating, Predicting, Learning

• The digestive organs are under the control of the nervous system
• Conditional reactions are involuntary associations - associative learning happens automatically without conscious involvement.
• At the same time as valence, the ability to use experience to change what is considered good and bad also emerges.
• Learning in biological brains has always been continual.
• Pavlov’s conditional reflexes are always strengthening (acquisition) or weakening (extinction) with each new experience. Extinction may be followed by spontaneous recovery (instantaneous) or reacquisition (faster than first time)
• Spontaneous recovery is a primitive form of long-term memory.
• The credit assignment problem - which cue really predicted something subsequently happening?:
  • Eligibility traces - Immediately follows cue
  • Overshadowing - Pick strongest cue
  • Latent inhibition - Pick the cue you haven’t seen before.
  • Blocking - Use existing cues and ignore others.
• Learning occurs when synapses change strength or when new ones are formed or old ones are removed.
• Association, prediction, and learning emerged to tweak the goodness and badness of things

Brain Parts

• Hypothalamus
• Thalamus
• Cerebellum - major role in motor control. May also be involved in cognitive functions, such as attention and language as well as emotional control

• Cerebral Hemispheres/Cerebral Cortex - concerned with higher mental functions: perception, action, language, and planning. Contains about 100 billion neurons, each with about a thousand synapses, making a total of about 100 trillion synaptic connections
  • Frontal lobe - part of the neural circuit governing social judgements, planning and organization of activities, aspects of language, control of movement, and a form of short-term memory called working memory
  • Parietal lobe - receives sensory information about touch, pressure, and space around the body and helps integrate that information into coherent perceptions
    • somatosensory cortex - a strip in the parietal lobe contains Wilder Penfield's sensory homunculus.
  • Occipital lobe in involved in vision
  • Temporal lobe is involved with auditory processing and aspects of language and memory.
  • Basal ganglia - help regulate motor performance
  • Hippocampus - involved with aspects of memory storage
  • Amygdala - coordinates autonomic and endocrine responses in the context of emotional states

Brain Functions

The brain provides coherent control over the actions of an animal. Information from the sense organs is collected in the brain, where it is processed to extract information about the structure of the environment. It combines the processed information with info about the current needs of the animal and with memory of past circumstances, and then generates motor responses. The main functions are:

• Perception - The brain collects info from the senses.
• Motor control - Motor systems are areas of the brain, mainly in the spinal cord and hindbrain, that initiate body movements by activating muscles.
• Sleep - The brain controls the transitions from sleeping to waking in a daily cycle
• Homeostasis - maintaining parameters (such as temperature, water content, salt concentration in the bloodstream, blood glucose levels, blood oxygen level) within a limited range of variation, through negative feedback
• Motivation - The brain activates behaviors to meet any needs that arise, generally through a reward-punishment mechanism. The basal ganglia inihibit most of the motor systems in the brain, and then release the inhibition for a specific motor system to allow its action to be carried out.
• Learning and memory - modifying behavior based on experience:
  • Working memory - maintaining a temporary representation of information about the task that you are currently working on
  • Episodic memory - remembering the details of specific events. The Hippocampus is heavily involved.
  • Semantic memory - remembering facts and relationships. Mainly in the Cerebral Cortex
  • Instrumental learning - allowing rewards and punishments to modify behavior
  • Motor learning - refining patterns of body movement by practicing or repetition