liveonearth (liveonearth) wrote,

Motor and Limbic Systems: the Cortico Striate Loops

Ventral tegmental dopamine neurons respond only to UNPREDICTED REWARDS. When the goodie is predictable, those particular dopamine cells stop firing. They's the ones that say "Oh YEAH" to something one discovers as enjoyable and satisfying. Smoking a cigarette fires those cells even when it's not unpredicted, it provokes that Oh YEAH chemistry every single time you light up.

It's the dopamine release in the nucleus accumbens that stengthens the links between the stimulus and the wanting. Wanting and liking are not the same.

-masses of gray matter (nuclei) surrounding the thalamus in the cerebral hemispheres
-"does some chosing"
-two primary functions: action selection and reinforcement learning
-groups neuronal populations so as to help focus attention on a desired motor response, and to switch in the context of novel cues, ie reinforcement (reward learning)
-parts: caudate, putamen, nucleus accumbens, globus pallidus (internal & external), subthalamic nucleus, substantia nigra, ventral tegementum
-the corpus STRIATUM is part of the basal ganglia: the caudate, putamen and nucleus accumbens
-the lenticular nucleus are: putamen and GLOBUS PALLIDUS (internal GPi and external GPe)
-the GPi usually inhibits the thalamus, but is disinhibited by the striatum in order to generate motor output (direct pathway)
-the indirect pathway involves subthalamic input to the GPi, increasing its usual inhibition of the thalamus and decreasing the motor output, especially: inhibits unintended movements
-the subthalamus is in the midbrain
-motor/cognitive cortical programs are funneled through the striatum and globus pallidus to refine motor and cognitive programs
-the cortex sends it motor programs to the striatum, the striatum consults the substantia nigra, then signals the globus palidus, which in turn consults the subthalamic nucleus. The globus pallidus signals the thalamus, which then signals the cortex again. If the thalamic message was "pick up that cup", the signal travels to the motor cortex which tells the brainstem to tell the spinal cord to tell us to pick up the cup, and how. But that's out of the loop. (old material)
-consultants: substantia nigra and subthalamus select "What is important", reinforce certain outputs, ignore many signals, generate chosen behavior. These are the "deciders".

-regulates the direct and indirect pathways
-increases signal-to-noise ratio in striatum (helps concentration) by enhancing strong inputs and suppressing weak ones
-when there's not enough dopamine in a loop it can result in OCD, obsessive-compulsive behavior due to the inability to switch tasks. Need dopamine to reprogram in basal ganglia.
-modulating: substantia nigra, pars compacta (SNpc) projects to striatum (black cells in midbrain cut)
-modulating: the SNpr is similar to the GPi
-modulating: ventral tegmentum to ventral striatum (nucleus accumbens) and prefrontal cortex
below here from book: Intoxicating Minds by Regan
--two groups of nerve cells in brain use dopamine: substantia nigra (motor control) and ventral tegmentum (evaluation of info in surroundings, excessive activity-->irrational)
--amphetamine pushes dopamine vesicles out of presynapse in ventral tegmentum
-->hyperactivity and restlessness
--excessive amphet use-->paranoid, delusional
--schizophrenia = too much dopamine
-how we determine behavior
-anatomically distinct pathways
-three covered here: the motor, association and limbic loops
-cortices of loops convey phasic excitator signals (bids for selection) to the striatal nuclei
-combined inputs from loops forms goals, actions and movements, ie. goal directed activity

-motor cortices project to putamen (in striatum)
-motor cortices include: primary motor, premotor, supplementary and somatosensory cortex
-putamen projects to globus pallidus to thalamus to cortex with updated programs
-programming is not sufficient, need initiation also to have movement
-programming involves exact directions, velocities and proportions of movements

-parietal and temporal association cortices project to caudate (in striatum)
-caudate to globus pallidus external to thalamus and back to cortex
-has executive function: select appropriate movements, allocate attention, plan, organize, regulate, monitor goal-directed behavior, switching behavioral set
-internally generated movements
-doesn't work in Parkinson's: can internally generate movements but can be externally triggered

-cortex involved: orbitofrontal, anterior cingulate, amygdala and hippocampus (are these all cortical?)
-limbic cortex (?) projects to nucleus accumbens (ventral striatum, part of caudate)
-peripheral contribution?? ventral striatum gets input from mesolimbic dopamine (??)
-nucleus accumbens projects to thalamus
-cortex to striatum to thalamus to cortex (bypass globus pallidus)
-declarative and episodic memory "I was there"
-forms habits, reward associations, addiction, attractions, "loves everything"
-as opposed to amygdala which dislikes, forms aversions, so why is amygdala in the list of contributing cortex?


regulate sleep and dreaming: regulate duration of REM/dream sleep

enlivens vigilance
enhances attention to stimuli
axons containing norepi come from 10,000 or so neurons in locus ceruleus
amygdala under lateral temporal lobe
when activated-->adrenaline released from adrenals-->stimulates locus coeruleus-->norepi

the raphe nucleus is close to the locus ceruleus and uses serotonin to modulate distant brain areas
both ser and norepi modulate mood
serotonin is esp low in individuals who attempt suicide by violent means
higher in those who attempt suicide by poison
thus Regan thinks it's related to violence, aggression
Tags: addiction, brain, cigarettes, dopamine, emotion, nervous system, neurotransmitters, serotonin, sleep, smoking, suicide

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