Connectionists: conditioning, dopamine, amygdala, hypothalamus, basal ganglia, orbitofrontal cortex

[Stephen Grossberg]

The following articles about reinforcement learning are now available 
at 
<http://cns-web.bu.edu/Profiles/Grossberg/>http://www.cns.bu.edu/~steve

Mark R. Dranias, Stephen Grossberg, and Daniel Bullock
Dopaminergic and Non-Dopaminergic Value Systems in Conditioning and 
Outcome-Specific Revaluation
Brain Research, in press.

ABSTRACT
Animals are motivated to choose environmental options that can best 
satisfy current needs.  To explain such choices, this paper 
introduces the MOTIVATOR (Matching Objects To Internal VAlues 
Triggers Option Revaluations) neural model.  MOTIVATOR describes 
cognitive-emotional interactions between higher-order sensory 
cortices and an evaluative neuraxis composed of the hypothalamus, 
amygdala, and orbitofrontal cortex.  Given a conditioned stimulus 
(CS), the model amygdala and lateral hypothalamus interact to 
calculate the expected current value of the subjective outcome that 
the CS predicts, constrained by the current state of deprivation or 
satiation.  The amygdala relays the expected value information to 
orbitofrontal cells that receive inputs from anterior inferotemporal 
cells, and medial orbitofrontal cells that receive inputs from rhinal 
cortex.  The activations of these orbitofrontal cells code the 
subjective values of objects.  These values guide behavioral choices. 
The model basal ganglia detect errors in CS-specific predictions of 
the value and timing of rewards.  Excitatory inputs from the 
pedunculopontine nucleus interact with timed inhibitory inputs from 
model striosomes in the ventral striatum to regulate dopamine burst 
and dip responses from cells in the substantia nigra pars compacta 
and ventral tegmental area.  Learning in cortical and striatal 
regions is strongly modulated by dopamine.  The model is used to 
address tasks that examine food-specific satiety, Pavlovian 
conditioning, reinforcer devaluation, and simultaneous visual 
discrimination. Model simulations successfully reproduce discharge 
dynamics of known cell types, including signals that predict saccadic 
reaction times and CS-dependent changes in systolic blood pressure.

Keywords:  amygdala, orbitofrontal cortex, rhinal cortex, lateral 
hypothalamus, inferotemporal cortex, basal ganglia, conditioning, 
motivation, devaluation, food-specific satiety, dopamine, 
cognitive-emotional interactions, decision-making, discrimination 
learning

******************
Stephen Grossberg, Daniel Bullock, and Mark R. Dranias
Neural Dynamics Underlying Impaired Autonomic and Conditioned 
Responses Following Amygdala and Orbitofrontal Lesions
Behavioral Neuroscience, in press.

ABSTRACT
A neural model is presented that explains how outcome-specific 
learning modulates affect, decision-making and Pavlovian conditioned 
approach responses.  The model addresses how brain regions 
responsible for affective learning and habit learning interact, and 
answers a central question: What are the relative contributions of 
the amygdala and orbitofrontal cortex to emotion and behavior?  In 
the model, the amygdala calculates outcome value while the 
orbitofrontal cortex influences attention and conditioned responding 
by assigning value information to stimuli.  Model simulations 
replicate autonomic, electrophysiological, and behavioral data 
associated with three tasks commonly used to assay these phenomena: 
Food consumption, Pavlovian conditioning, and visual discrimination. 
Interactions of the basal ganglia and amygdala with sensory and 
orbitofrontal cortices enable the model to replicate the complex 
pattern of spared and impaired behavioral and emotional capacities 
seen following lesions of the amygdala and orbitofrontal cortex. 

Keywords: Pavlovian conditioning, inferotemporal and rhinal cortex, 
amygdala, basal ganglia, orbitofrontal cortex