Delve into the fascinating world of dopamine and its role in shaping our behavior and motivation. From the pleasure centers of the brain to the intricate pathways of reinforcement and conditioning, this document offers invaluable insights into how our brains process rewards and punishments. Explore...
Dopamine: pleasure and motivation
Every single sensory input or internal pattern of activity in the brain will bounce off the subcortical
structures in charge of evaluating its possible vital and hedonic relevance, and its possible emotional
meaning a motivational nature.
In the amygdala the assessment of vital relevance is performed. It’s a quantitative analysis, meaning
that it recognizes the intensity of any kind of emotion. Generally, it will be activated more by a negative
emotion, as it would require a prompter and bigger response, in order to survive.
In the VTA (ventral tegmental area of the midbrain) the emotional “colour” (hedonic value, good/bad)
of the cues is assessed:
• VTA projects to the n. accumbens (ventral striatum) eliciting pleasure, gratification,
reinforcement (learning) (mesolimbic path, reward path). Nucleus accumbens fires both
when you obtain a reward (pleasure), and when a reward becomes possible (expectation of a
pleasure) à plays an important role in motivation (showing a sandwich to someone hungry
makes him even more hungry, evening before Christmas is even better than Christmas day,
need to pee after you see a toilet is increased etc.)
• VTA projects to the prefrontal cortex to enhance of cortical activities (imagination and
planning) related to the cue (motivation to interactive behaviour) (mesocortical path)
In the SNpc (substantia nigra pars compacta, also in the midbrain) the emotional “operational” value
of the cue is assessed
• substantia nigra pars compacta projects to the dorsal striatum to regulate the initiation,
reconciliation, harmonization, shifting and choice among motor and cognitive behaviours
SNpc this way drives the inattentive motor and cognitive behaviour
• dopaminergic control by the SNpc induces plastic changes in striatal circuitry that produce the
development of heuristics (experience-based “spontaneous” responses)
In the raphe, serotonergic projections will establish a scale that defines the different levels and kinds of
pleasure based on the weights of different motivational values in decision making (self-
interest, sense of justice, social appreciation, self-image, future vs. momentary advantage). In addition
to this the serotonergic projections will perform the exam of reality, to assess consistency and likelihood
that something happens (expectation/hope vs. realism).
Dopaminergic neurons are involved in processing by both VTA and SNpc:
1. mesolimbic path: from the VTA to the ventral striatum (n. accumbens)
2. mesocortical path: from the VTA to the prefrontal cortex
3. nigro-striatal path: from the SNpc to medium spiny neurons (MSN) in the dorsal striatum -
projections to D1 facilitatory receptors on dynorphin / substance P positive MSN that give rise
to the direct, disinhibitory, path, and to D2 inhibitory receptors on enkephalin / neurotensin
positive MSN that originate the indirect, inhibitory path
4. a fourth dopaminergic path in the brain is involved in endocrine control: dopamine is the
prolactin inhibitory factor (PIF) released through the tubero-infundibular path from the
hypothalamus into the anterior pituitary portal circulation
222 Body At Work II
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