Andrew M Clark

Publications (2)14.23 Total impact

• Article: Interaction between orbital prefrontal and rhinal cortex is required for normal estimates of expected value.

  Andrew M Clark, Sebastien Bouret, Adrienne M Young, Elisabeth A Murray, Barry J Richmond
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  ABSTRACT: Predicting and valuing potential rewards requires integrating sensory, associative, and contextual information with subjective reward preferences. Previous work has identified regions in the prefrontal cortex and medial temporal lobe believed to be important for each of these functions. For example, activity in the orbital prefrontal cortex (PFo) encodes the specific sensory properties of and preferences for rewards, while activity in the rhinal cortex (Rh) encodes stimulus-stimulus and stimulus-reward associations. Lesions of either structure impair the ability to use visual cues or the history of previous reinforcement to value expected rewards. These areas are linked via reciprocal connections, suggesting it might be their interaction that is critical for estimating expected value. To test this hypothesis, we interrupted direct, intra-hemispheric PFo-Rh interaction in monkeys by performing crossed unilateral ablations of these regions (functional disconnection). We asked whether this circuit is crucial primarily for cue-reward association or for estimating expected value per se, by testing these monkeys, as well as intact controls, on tasks in which expected value was either visually cued or had to be inferred from block-wise changes in reward size in uncued trials. Functional disconnection significantly affected performance in both tasks. Specifically, monkeys with functional disconnection showed less of a difference in error rates and reaction times across reward sizes, in some cases behaving as if they expected rewards to be of equal magnitude. These results support a model whereby information about rewards signaled in PFo is combined with associative and contextual information signaled within Rh to estimate expected value.
  Journal of Neuroscience 01/2013; 33(5):1833-45. · 7.11 Impact Factor
• Article: Intersection of reward and memory in monkey rhinal cortex.

  Andrew M Clark, Sebastien Bouret, Adrienne M Young, Barry J Richmond
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  ABSTRACT: In humans and other animals, the vigor with which a reward is pursued depends on its desirability, that is, on the reward's predicted value. Predicted value is generally context-dependent, varying according to the value of rewards obtained in the recent and distant past. Signals related to reward prediction and valuation are believed to be encoded in a circuit centered around midbrain dopamine neurons and their targets in the prefrontal cortex and basal ganglia. Notably absent from this hypothesized reward pathway are dopaminergic targets in the medial temporal lobe. Here we show that a key part of the medial temporal lobe memory system previously reported to be important for sensory mnemonic and perceptual processing, the rhinal cortex (Rh), is required for using memories of previous reward values to predict the value of forthcoming rewards. We tested monkeys with bilateral Rh lesions on a task in which reward size varied across blocks of uncued trials. In this experiment, the only cues for predicting current reward value are the sizes of rewards delivered in previous blocks. Unexpectedly, monkeys with Rh ablations, but not intact controls, were insensitive to differences in predicted reward, responding as if they expected all rewards to be of equal magnitude. Thus, it appears that Rh is critical for using memory of previous rewards to predict the value of forthcoming rewards. These results are in agreement with accumulating evidence that Rh is critical for establishing the relationships between temporally interleaved events, which is a key element of episodic memory.
  Journal of Neuroscience 05/2012; 32(20):6869-77. · 7.11 Impact Factor