Biomedical subjects

Matthew R Roesch

Publications and source records attributed to Matthew R Roesch.

11 recordsLinked to original sources

PubMed2007

Previous cocaine exposure makes rats hypersensitive to both delay and reward magnitude.

Animals prefer an immediate over a delayed reward, just as they prefer a large over a small reward. Exposure to psychostimulants causes long-lasting changes in structures critical for this behavior and might disrupt normal time-discounting performance. To test this hypothesis, we exposed rats to cocaine daily for 2 weeks (30 mg/kg, i.p.). Approximately 6 weeks later, we tested them on a variant of a time-discounting task, in which the rats responded to one of two locations to obtain reward while we independently manipulated the delay to reward and reward magnitude. Performance did not differ between cocaine-treated and saline-treated (control) rats when delay lengths and reward magnitudes were equal at the two locations. However, cocaine-treated rats were significantly more likely to shift their responding when we increased the delay or reward size asymmetrically. Furthermore, they were slower to respond and made more errors when forced to the side associated with the lower value. We conclude that previous exposure to cocaine makes choice behavior hypersensitive to differences in the time to and size of available rewards, consistent with a general effect of cocaine exposure on reward valuation mechanisms.

Animals↗

PubMed2006

Encoding of time-discounted rewards in orbitofrontal cortex is independent of value representation.

We monitored single-neuron activity in the orbitofrontal cortex of rats performing a time-discounting task in which the spatial location of the reward predicted whether the delay preceding reward delivery would be short or long. We found that rewards delivered after a short delay elicited a stronger neuronal response than those delivered after a long delay in most neurons. Activity in these neurons was not influenced by reward size when delays were held constant. This was also true for a minority of neurons that exhibited sustained increases in firing in anticipation of delayed reward. Thus, encoding of time-discounted rewards in orbitofrontal cortex is independent of the encoding of absolute reward value. These results are contrary to the proposal that orbitofrontal neurons signal the value of delayed rewards in a common currency and instead suggest alternative proposals for the role this region plays in guiding responses for delayed versus immediate rewards.

Action Potentials↗

PubMed2006

Associative encoding in posterior piriform cortex during odor discrimination and reversal learning.

Recent proposals have conceptualized piriform cortex as an association cortex, capable of integrating incoming olfactory information with descending input from higher order associative regions such as orbitofrontal cortex and basolateral amygdala (ABL). If true, encoding in piriform cortex should reflect associative features prominent in these areas during associative learning involving olfactory cues. We recently reported that neurons in anterior piriform cortex (APC) in rats exhibited significant plasticity in their responses to odor cues during associative learning. Here, we have repeated this study, recording from neurons in posterior piriform cortex (PPC), a region of piriform cortex that receives much stronger input from ABL. If associative encoding in piriform cortex is driven by inputs from ABL, then we should see more plasticity in PPC neurons than we observed in APC. Consistent with this hypothesis, we found that PPC neurons were highly associative and appeared to be somewhat more likely than neurons recorded in APC to alter their responses to the odor cues after reversal of the odor-outcome associations in the task. Further, odor-selective PPC populations exhibited markedly different firing patterns based on the valence of the odor cue. These results suggest associative encoding in piriform cortex is represented in a topographical fashion, reflecting the stronger and more specific input from olfactory bulb concerning the sensory features of odors in anterior regions and stronger input from ABL concerning the meaning of odors in posterior regions.

Amygdala↗

PubMed2006

Associative encoding in anterior piriform cortex versus orbitofrontal cortex during odor discrimination and reversal learning.

Recent proposals have conceptualized piriform cortex as an association cortex, capable of integrating incoming olfactory information with descending input from higher order associative regions such as orbitofrontal cortex (OFC). If true, encoding in piriform cortex should reflect associative features prominent in these areas during associative learning involving olfactory cues. To test this hypothesis, we recorded from neurons in OFC and anatomically related parts of the anterior piriform cortex (APC) in rats, learning and reversing novel odor discriminations. Findings in OFC were similar to what we have reported previously, with nearly all the cue-selective neurons exhibiting substantial plasticity during learning and reversal. Also, many of the cue-selective neurons were originally responsive in anticipation of the outcomes early in learning, thereby providing a single-unit representation of the cue-outcome associations. Some of these features were also evident in firing activity in APC, including some plasticity across learning and reversal. However, APC neurons failed to reverse cue selectivity when the associated outcome was changed, and the cue-selective population did not include neurons that were active prior to outcome delivery. Thus, although representations in APC are substantially more associative than expected in a purely sensory region, they do appear to be somewhat more constrained by the sensory features of the odor cues than representations in downstream areas of OFC.

Animals↗

PubMed2006

Orbitofrontal cortex, decision-making and drug addiction.

The orbitofrontal cortex, as a part of prefrontal cortex, is implicated in executive function. However, within this broad region, the orbitofrontal cortex is distinguished by its unique pattern of connections with crucial subcortical associative learning nodes, such as basolateral amygdala and nucleus accumbens. By virtue of these connections, the orbitofrontal cortex is uniquely positioned to use associative information to project into the future, and to use the value of perceived or expected outcomes to guide decisions. This review will discuss recent evidence that supports this proposal and will examine evidence that loss of this signal, as the result of drug-induced changes in these brain circuits, might account for the maladaptive decision-making that characterizes drug addiction.

Animals↗

PubMed2006

Abnormal associative encoding in orbitofrontal neurons in cocaine-experienced rats during decision-making.

Recent evidence has linked exposure to addictive drugs to an inability to employ information about adverse consequences, or outcomes, to control behavior. For instance, addicts and drug-experienced animals fail to adapt their behavior to avoid adverse outcomes in gambling and reversal tasks or after changes in the value of expected rewards. These deficits are similar to those caused by damage to the orbitofrontal cortex, suggesting that addictive drugs may cause long-lasting changes in the representation of outcome associations in a circuit that includes the orbitofrontal cortex. Here we test this hypothesis by recording from orbitofrontal neurons in a discrimination task in rats previously exposed to cocaine (30 mg/kg i.p. for 14 days). We found that orbitofrontal neurons recorded in cocaine-experienced rats failed to signal the adverse outcome at the time a decision was made in the task. The loss of this signal was associated with abnormal changes in response latencies on aversive trials. Furthermore, upon reversal of the cue-outcome associations, orbitofrontal neurons in cocaine-treated rats with enduring reversal impairments failed to reverse their cue-selectivity, while orbitofrontal neurons in cocaine-treated rats with normal performance showed an increase in the plasticity of cue-selective firing after reversal. These results provide direct neurophysiological evidence that exposure to cocaine can cause behaviorally relevant changes in the processing of associative information in a circuit that includes the orbitofrontal cortex.

Animals↗

PubMed2005

Neuronal activity in primate orbitofrontal cortex reflects the value of time.

Neurons in monkey orbitofrontal cortex (OF) are known to respond to reward-predicting cues with a strength that depends on the value of the predicted reward as determined 1) by intrinsic attributes including size and quality and 2) by extrinsic factors including the monkey's state of satiation and awareness of what other rewards are currently available. We pose here the question whether another extrinsic factor critical to determining reward value-the delay expected to elapse before delivery-influences neuronal activity in OF. To answer this question, we recorded from OF neurons while monkeys performed a memory-guided saccade task in which a cue presented early in each trial predicted whether the delay before the monkey could respond and receive a reward of fixed size would be short or long. OF neurons tended to fire more strongly in response to a cue predicting a short delay. The tendency to fire more strongly in anticipation of a short delay was correlated across neurons with the tendency to fire more strongly before a large reward. We conclude that neuronal activity in OF represents the time-discounted value of the expected reward.

Action Potentials↗

PubMed2005

Neuronal activity dependent on anticipated and elapsed delay in macaque prefrontal cortex, frontal and supplementary eye fields, and premotor cortex.

In macaque monkeys performing a memory-guided saccade task for a reward of variable size, neuronal activity in several areas of frontal cortex is stronger when the monkey anticipates a larger reward. This effect might depend on either the size or the value of the reward. To distinguish between these possibilities, we recorded from neurons in frontal cortex while controlling value through a manipulation of time rather than amount. A cue presented at the beginning of each trial, predicted the length of the delay during which the monkey would have to maintain fixation before performing a saccade and receiving a reward of fixed size. Predicting a short delay had effects closely similar to those of predicting a large reward: 1) monkeys were more motivated when working for a reward at short delay, 2) neurons tended to fire more strongly before a short delay, 3) individual neurons firing more strongly before a short delay tended also to fire more strongly before a large reward, and 4) the tendency to fire more strongly before a short delay was far more pronounced in premotor areas caudal to the arcuate sulcus than in association areas rostral to it. The association areas, in contrast, were marked by a tendency for neurons to fire more strongly at the end of the long delay. We conclude that predicting a short delay, like predicting a large reward, induces an enhancement of neuronal activity related to motivational modulation of the monkey's preparatory state.

Animals↗

PubMed2004

Neuronal activity in macaque SEF and ACC during performance of tasks involving conflict.

It has been suggested on the basis of previous studies involving functional MRI (fMRI) and single-neuron recording that neurons of the supplementary eye field (SEF) and anterior cingulate cortex (ACC) monitor conflict. To test this idea, we carried out microelectrode recording in monkeys performing a color-conditional eye movement task in which red and green cues instructed leftward and rightward saccades, respectively. In a variant inducing conflict by spatial incompatibility, the cue was presented either at the location of the target (no conflict) or opposite the location of the target (conflict). In a variant inducing conflict by reversal, the foveal cue either remained one color (no conflict) or reversed color after 100 ms (conflict), with the monkey required to follow the instruction conveyed by the second color. In both tasks, conflict was evident in behavioral measures (reduced percent correct and slowed reaction time) and in physiological measures (reduced strength of directional activity among direction-selective neurons). In the SEF, there was a tendency for neurons to fire more strongly on trials involving conflict, but this effect took the form of modulation of task-related activity among direction-selective neurons, not of a pure conflict-monitoring signal. In the ACC, there was no conflict-related enhancement. These results are incompatible with the idea that the SEF and ACC contain populations of neurons specialized for monitoring conflict.

Action Potentials↗

PubMed2004

Neuronal activity related to reward value and motivation in primate frontal cortex.

In several areas of the macaque brain, neurons fire during delayed-response tasks at a rate determined by the value of the reward expected at the end of the trial. The activity of these neurons might be related to the value of the expected reward or to the degree of motivation induced by expectation of the reward. We describe results indicating that the nature of reward-dependent activity varies across areas. Neuronal activity in orbitofrontal cortex represents the value of the expected reward, whereas neuronal activity in premotor cortex reflects the degree of motivation.

Action Potentials↗

PubMed2003

Impact of expected reward on neuronal activity in prefrontal cortex, frontal and supplementary eye fields and premotor cortex.

In several regions of the macaque brain, neurons fire during delayed response tasks at a rate determined by the value of the reward expected at the end of the trial. The activity of these neurons might be related either to the internal representation of the appetitive value of the expected reward or to motivation-dependent variations in the monkey's level of motor preparation or motor output. According to the first interpretation, reward-related activity should be most prominent in areas affiliated with the limbic system. According to the second interpretation, it should be most prominent in areas affiliated with the motor system. To distinguish between these alternatives, we carried out single-neuron recording while monkeys performed a memory-guided saccade task in which a visual cue presented early in each trial indicated whether the reward would be large or small. Neuronal activity accompanying task performance was monitored in the dorsolateral prefrontal cortex (PFC), the frontal eye field (FEF), a transitional zone caudal to the frontal eye field (FEF/PM), premotor cortex (PM), the supplementary eye field (SEF), and the rostral part of the supplementary motor area (SMAr). The tendency for neuronal activity to increase after cues that predicted a large reward became progressively stronger in progressively more posterior areas both in the lateral sector of the frontal lobe (PFC < FEF < FEF/PM < PM) and in the medial sector (SEF < SMAr). The very strong reward-related activity of premotor neurons was presumably attributable to the monkey's motivation-dependent level of motor preparation or motor output. This finding points to the need to determine whether reward-related activity in other nonlimbic brain areas, including dorsolateral prefrontal cortex and the dorsal striatum, genuinely represents the value of the expected reward or, alternatively, is related to motivational modulation of motor signals.

Action Potentials↗