Please enable JavaScript.
Coggle requires JavaScript to display documents.
Dopamine, Reward and Reinforcement (ACC (Another major target of dopamine…
Dopamine, Reward and Reinforcement
involved in learning, cognition, behaviour
-
Dopamine neurons
-
Learning
-
before task, dopamine neurons responded to unpredicted rewards
during learning reward became increasingly predictable and neuronal activity gradually decreased to baseline levels
-
When expected rewards were omitted, there was a phasic decrease in activity at the time that the reward was expected
During learning the dopamine response switched from the reward (US) to the reward predictor (CS) Schultz et al 1997
-
-
Human VTA
D'Ardenne et al 2008
Task: Guess whether the number on the right of the screen would be greater or less than the number on the left (max 10).
-
-
They found activity in the VTA that increased when they unexpectedly got the $1 and was greater as the probability of reward decreased
-
Against classical view
-
And further studies have shown a role for dopamine in effort-based decision-making (see Phillips, Walton et al., 2007)
Other studies have shown that dopamine neurons signal during cognitive tasks, which doesn’t fit with the classical view (Matsumoto & Takada, 2013)
Some studies have extended the hypothesis to include other influences being integrated with reward prediction, such as goaldirected movement (Syed et al., 2016)
-
Striatum
-
-
-
-
• Ventral:
nucleus accumbens
Pessiglione et al., (2006)
-
-
-
-
-
conclude that dopamine-dependent modulation of striatal activity can account for how the human brain uses reward prediction errors to improve future decisions.
Furthermore, the findings might provide insight into models of clinical disorders in which dopamine is implicated, and for which L-DOPA and haloperidol are used as therapeutic agents, such as Parkinson's disease and schizophrenia
For example, it offers a potential mechanism for the development of compulsive behaviours (such as overeating, hypersexuality and pathological gambling) induced by dopamine replacement therapy in patients with Parkinson's disease
-
ACC
-
Engaged by many different processes, but also contains neurons which respond to rewarding stimuli.
Recorded from the ACC when monkeys were making choices between reward probabilities (Kennerley et al 2011)
They found neurons that responded to positive PEs, separate neurons that responded to negative PEs and a third set of neurons that responded to both.
fMRI in humans performing task where there is a subgoal leading to an overall rewarding outcome (Ribas-Fernandes 2011)
-
-
Drugs as rewards
Rats hooked up intravenously or intracranially to to equipment that allows for dopamine to be released when they make a lever press (an operant response)
Do drugs modify responses to natural rewards or constitute rewards in their own right – engaging existing mechanisms?
Over time rats start to repeatedly self-administer dopamine to themselves. They find dopamine, in itself, rewarding
Cocaine works directly on dopamine neurons by blocking dopamine re-uptake and hence increasing the concentration of dopamine at the synapse
Drugs of abuse that mimic or boost the phasic dopamine reward prediction error might generate a powerful teaching signal and might even produce behavioural changes
Rats and temporal coding - cocaine quicker, marijuana slower
-
-
Reading
Behrens et al 2008
Social learning is widely held to be distinct from other forms of learning in its mechanism and neural implementation; it is often assumed to compete with simpler mechanisms, such as reward-based associative learning, to drive behaviour
Recently, neural signals have been observed during social exchange reminiscent of signals seen in studies of associative learning
We find that key computational variables for learning in the social and reward domains are processed in a similar fashion, but in parallel neural processing streams
Two neighbouring divisions of the anterior cingulate cortex were central to learning about social and reward-based information, and for determining the extent to which each source of information guides behaviour
When making a decision, however, the information learnt using these parallel streams was combined within ventromedial prefrontal cortex
These findings suggest that human social valuation can be realized by means of the same associative processes previously established for learning other, simpler, features of the environment.
D'Ardenne et al. 2008
-
Although studies in nonhuman species provide direct support for this theory, fMRI studies in humans have focused on brain areas targeted by dopamine neurons (ventral striatum) rather than on brainstem dopaminergic nuclei (VTA) and substantia nigra.
When primary rewards were used in an experiment, the VTA blood oxygen level-dependent (BOLD) response reflected a positive reward prediction error, whereas the VStr encoded positive and negative reward prediction errors
When monetary gains and losses were used, VTA BOLD responses reflected positive reward prediction errors modulated by the probability of winning
-
