Sat, 26 Jul 2008 03:15:45 BST CiteULike: nelmor Lau http://www.citeulike.org/user/nelmor/author/Lau CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/nelmor/article/2987293 <i>Neuron, Vol. 59, No. 1. (10 July 2008), pp. 6-8.</i><br /><br />Although noncholinergic neurons in the basal forebrain are known to contribute to cognition, their response properties in behaving animals is unclear. In this issue of Neuron, Lin and Nicolelis demonstrate that these neurons represent the motivational salience of sensory stimuli and may modulate cortical processing to direct top-down attention. Noncholinergic Neurons in the Basal Forebrain: Often Neglected but Motivationally Salient Brian Lau Daniel Salzman doi:10.1016/j.neuron.2008.06.017 Neuron, Vol. 59, No. 1. (10 July 2008), pp. 6-8. 2008-07-11T08:24:44-00:00 2008 Neuron 59 1 6 8 basal_forrbrain nnv salience value http://www.citeulike.org/user/nelmor/article/2770526 <i>Neuron, Vol. 58, No. 3. (8 May 2008), pp. 451-463.</i><br /><br />Summary Choosing the most valuable course of action requires knowing the outcomes associated with the available alternatives. The striatum may be important for representing the values of actions. We examined this in monkeys performing an oculomotor choice task. The activity of phasically active neurons (PANs) in the striatum covaried with two classes of information: action-values and chosen-values. Action-value PANs were correlated with value estimates for one of the available actions, and these signals were frequently observed before movement execution. Chosen-value PANs were correlated with the value of the action that had been chosen, and these signals were primarily observed later in the task, immediately before or persistently after movement execution. These populations may serve distinct functions mediated by the striatum: some PANs may participate in choice by encoding the values of the available actions, while other PANs may participate in evaluative updating by encoding the reward value of chosen actions. Value Representations in the Primate Striatum during Matching Behavior Brian Lau Paul Glimcher doi:10.1016/j.neuron.2008.02.021 Neuron, Vol. 58, No. 3. (8 May 2008), pp. 451-463. 2008-05-08T09:40:23-00:00 2008 Neuron 58 3 451 463 decision matching monkeys striatum value http://www.citeulike.org/user/nelmor/article/2175092 <i>J. Neurosci., Vol. 27, No. 52. (26 December 2007), pp. 14502-14514.</i><br /><br />The basal ganglia appear to have a central role in reinforcement learning. Previous experiments, focusing on activity preceding movement execution, support the idea that dorsal striatal neurons bias action selection according to the expected values of actions. However, many phasically active striatal neurons respond at a time too late to initiate or select movements. Given the data suggesting a role for the basal ganglia in reinforcement learning, postmovement activity may therefore reflect evaluative processing important for learning the values of actions. To better understand these postmovement neurons, we determined whether individual striatal neurons encode information about saccade direction, whether a reward had been received, or both. We recorded from phasically active neurons in the caudate nucleus while monkeys performed a probabilistically rewarded delayed saccade task. Many neurons exhibited peak responses after saccade execution (77 of 149) that were often tuned for the direction of the preceding saccade (61 of 77). Of those neurons responding during the reward epoch, one subset showed direction tuning for the immediately preceding saccade (43 of 60), whereas another subset responded differentially on rewarded versus unrewarded trials (35 of 60). We found that there was relatively little overlap of these properties in individual neurons. The encoding of action and outcome was performed by largely separate populations of caudate neurons that were active after movement execution. Thus, striatal neurons active primarily after a movement appear to be segregated into two distinct groups that provide complimentary information about the outcomes of actions. 10.1523/JNEUROSCI.3060-07.2007 Action and Outcome Encoding in the Primate Caudate Nucleus Brian Lau Paul Glimcher doi:10.1523/JNEUROSCI.3060-07.2007 J. Neurosci., Vol. 27, No. 52. (26 December 2007), pp. 14502-14514. 2007-12-27T13:19:51-00:00 2007 J. Neurosci. 27 52 14502 14514 action-selection monkeys reward saccade striatum value http://www.citeulike.org/user/nelmor/article/1466896 <i>J Neurophysiol (5 July 2007), 01140.2006.</i><br /><br />Work in behaving primates indicates that midbrain dopamine neurons encode a prediction error, the difference between an obtained reward and the reward expected. Studies of dopamine action potential timing in the alert and anaesthetized rat indicate that dopamine neurons respond in tonic and phasic modes, a distinction that has been less well characterized in the primates. We used spike train models to examine the relationship between the tonic and burst modes of activity in dopamine neurons while monkeys were performing a reinforced visuo-saccadic movement task. We studied spiking activity during four task-related intervals; two of these were intervals during which no task-related events occurred, while two were periods marked by task-related phasic activity. We found that dopamine neuron spike trains during the intervals when no events occurred were well described as tonic. Action potentials appeared to be independent, to occur at low frequency, and to be almost equally well described by Gaussian and Poisson-like (Gamma) processes. Unlike in the rat, interspike intervals as low as 20 ms were often observed during these presumptively tonic epochs. Having identified these periods of presumptively tonic activity we were able to quantitatively define phasic modulations (both increases and decreases in activity) during the intervals in which task-related events occurred. This analysis revealed that the phasic modulations of these neurons include both bursting, as has been described previously, and pausing. Together bursts and pauses seemed to provide a continuous, although non-linear, representation of the theoretically defined reward prediction error of reinforcement learning. 10.1152/jn.01140.2006 Statistics of Midbrain Dopamine Neuron Spike Trains in the Awake Primate Hannah Bayer Brian Lau Paul Glimcher doi:10.1152/jn.01140.2006 J Neurophysiol (5 July 2007), 01140.2006. 2007-07-19T11:11:14-00:00 2007 J Neurophysiol 01140.2006 analysis dopamine monkeys http://www.citeulike.org/user/nelmor/article/1319011 <i>Science, Vol. 316, No. 5826. (11 May 2007), pp. 904-906.</i><br /><br />Unconscious motivation in humans is often inferred but rarely demonstrated empirically. We imaged motivational processes, implemented in a paradigm that varied the amount and reportability of monetary rewards for which subjects exerted physical effort. We show that, even when subjects cannot report how much money is at stake, they nevertheless deploy more force for higher amounts. Such a motivational effect is underpinned by engagement of a specific basal forebrain region. Our findings thus reveal this region as a key node in brain circuitry that enables expected rewards to energize behavior, without the need for the subjects`awareness. 10.1126/science.1140459 How the Brain Translates Money into Force: A Neuroimaging Study of Subliminal Motivation Mathias Pessiglione Liane Schmidt Bogdan Draganski Raffael Kalisch Hakwan Lau Ray Dolan Chris Frith doi:10.1126/science.1140459 Science, Vol. 316, No. 5826. (11 May 2007), pp. 904-906. 2007-05-22T08:39:27-00:00 2007 Science 316 5826 904 906 fmri reward ventral-pallidum