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Biomedical subjects

Robert D Rogers

Publications and source records attributed to Robert D Rogers.

14 recordsLinked to original sources
PubMed2007

Manipulating the experienced onset of intention after action execution.

Using transcranial magnetic stimulation (TMS), we have tested the time needed for the perceived onset of spontaneous motor intention to be fully determined. We found that TMS applied over the presupplementary motor area after the execution of a simple spontaneous action shifted the perceived onset of the motor intention backward in time, and shifted the perceived time of action execution forward in time. The size of the effect was similar regardless of whether TMS was applied immediately after the action or 200 msec after. The results of three control studies suggest that this effect is time-limited, specific to modality, and also specific to the anatomical site of stimulation. We conclude that the perceived onset of intention depends, at least in part, on neural activity that takes place after the execution of action. A model, which is based on the mechanism of cue integration under the presence of noise, is offered to explain the results. The implications for the conscious control of spontaneous actions are discussed.

Evoked Potentials, Motor↗
PubMed2006

The effects of low doses of delta-9 tetrahydrocannabinol on reinforcement processing in the risky decision-making of young healthy adults.

Research suggests that risky decision-making is sensitive to neuromodulatory influences acting upon corticolimbic circuitry. However, while other evidence attests to effects of delta-9 tetrahydrocannabinol (THC) on the activity of reward pathways, relatively little is known about the possible involvement of cannabinoid activity in risky choice. In this experiment, we examined the effects of a single sublingual 5 mg dose of THC on a test of risky decision-making (requiring choices between simultaneously presented gambles differing in their magnitude of gains, magnitude of losses and the probability with which these outcomes were delivered). Tests of non-normative decision-making involving risk-aversion when deciding between gains and risk-seeking choices when deciding between losses were also included. In all, 15 healthy adults were administered 5 mg THC and placebo in a double-blind, placebo-controlled, within-subject, cross-over design. THC had three principal effects relative to placebo: (i) THC reduced choice of gambles with variable gains and losses, but increased choice of gambles with zero-expected value; (ii) THC reduced participants' attention towards losses when the probability of winning was low (and the probability of losing was high); and (iii) THC speeded participants' responses to gambles with large compared to small potential gains. These results suggest that THC mediates specific motivational processes and the processing of reinforcement cues during risky choice, perhaps reflecting altered CB1 receptor or catecholamine activity within corticolimbic pathways.

Adult↗
PubMed2006

The effect of polymorphism at the serotonin transporter gene on decision-making, memory and executive function in ecstasy users and controls.

RATIONALE: 3, 4-Methylenedioxymethamphetamine (MDMA or "ecstasy") is a popular drug of abuse known to result in depletions of the serotonin (5-HT) system. A number of studies have reported that ecstasy users differ from controls on a variety of measures of cognitive function. However, the literature is not consistent and many negative findings were also reported. One reason for such inconsistency might be interindividual variance in vulnerability to the deleterious effects of ecstasy due to a number of factors, both genetic and environmental. OBJECTIVES: To investigate the hypothesis that carriers of the s allele at the 5-HT transporter gene-linked polymorphic region (5-HTTLPR), which was associated with reduced serotonergic neurotransmission relative to the l allele, would be most vulnerable to the effects of ecstasy on cognitive function. METHODS: We assessed memory, decision-making, and executive function in ecstasy users and controls, stratifying by genotype at the 5-HTTLPR. RESULTS: We observed that the 5-HTTLPR genotype groups differed on a number of measures in both the ecstasy users and the controls. While performing a risky decision-making task, ss and ls controls attended to differences in the probability of winning chosen gambles to a greater extent than the ll controls. However, this difference was dramatically attenuated in the ss ecstasy users. Furthermore, independent of ecstasy use, volunteers of the ss genotype outperformed the ll genotype on a visual planning task. CONCLUSIONS: The results are consistent with the hypothesis that cognitive impairment in ecstasy users may depend on genetic variation at the 5-HTTLPR.

Case-Control Studies↗
PubMed2006

On measuring the perceived onsets of spontaneous actions.

We investigated the neural mechanisms underlying the timing procedure that was devised by Libet et al. (1983) to measure the onset of conscious motor intentions in spontaneous actions. We previously showed that, when participants were required to estimate the onset of their intentions using this procedure, the activity in the presupplementary motor area (pre-SMA) was enhanced. Here, we show that when participants were required to estimate the onset of their motor executions (instead of their intentions), the activity in the cingulate motor area was enhanced. Across participants, the degree of this neural enhancement was correlated with the degree of perceptual bias: the higher the degree of enhancement, the earlier the perception. Analysis of data from a previous experiment suggests that the same principle holds true for the relationship between the perceived onset of intentions and the activity in the pre-SMA. We therefore argue that the timing method of Libet et al. (1983) is problematic, because the measuring process affects the neural representations of action and thus also the perceived onsets that the method is designed to measure.

Attention↗
PubMed2006

Low doses of delta-9 tetrahydrocannabinol (THC) have divergent effects on short-term spatial memory in young, healthy adults.

Evidence suggests that manipulating spatial information within working memory depends upon a circuitry organized around the prefrontal cortex (PFC) and the activity of the catecholamine systems. Other evidence attests to the effects of Delta-9 tetrahydrocannabinol (THC) on short-term spatial memory function, most probably involving CB(1) receptor activity within hippocampal circuitries. At the current time, there have been no systematic studies of the effects of THC on spatial working memory in human subjects using tasks known to depend upon frontotemporal neural circuitries. We examined the effects of a single sublingual 5 mg dose of THC on a test of spatial working memory (requiring active manipulation of remembered spatial information for the management of future behavior) and a test of spatial span (requiring only the reproduction of sequences of previously presented spatial cues). In all, 19 healthy adults were administered 5 mg THC and placebo in a double-blind, placebo-controlled, within-subject, crossover design. Male participants performed more accurately than female participants. THC significantly enhanced spatial working memory performance of female participants. By contrast, male and female participants produced more intrusion errors during performance of the Spatial Span task. These results suggest that THC has relatively complex effects on spatial memory in human subjects, perhaps reflecting altered CB(1) receptor activity within frontotemporal circuits or altered activity of mesocortical dopaminergic pathways in PFC areas associated with spatial memory.

Adult↗
PubMed2006

Effects of tryptophan depletion on the performance of an iterated Prisoner's Dilemma game in healthy adults.

Adaptive social behavior often necessitates choosing to cooperate with others for long-term gains at the expense of noncooperative behaviors giving larger immediate gains. Although little is know about the neural substrates that support cooperative over noncooperative behaviors, recent research has shown that mutually cooperative behavior in the context of a mixed-motive game, the Prisoner's Dilemma (PD), is associated with increased neural activity within reinforcement circuitry. Other research attests to a role for serotonin in the modulation of social behavior and in reward processing. In this study, we used a within-subject, crossover, double-blind design to investigate performance of an iterated, sequential PD game for monetary reward by healthy human adult participants following ingestion of an amino-acid drink that either did (T+) or did not (T-) contain l-tryptophan. Tryptophan depletion produced significant reductions in the level of cooperation shown by participants when playing the game on the first, but not the second, study days. This effect was accompanied by a significantly diminished probability of cooperative responding given previous mutually cooperative behavior. These data suggest that serotonin plays a significant role in the acquisition of socially cooperative behavior in human adult participants, and suggest novel hypotheses concerning the serotonergic modulation of reward information in socially cooperative behavior in both health and psychiatric illness.

Brain↗
PubMed2005

Neuropsychological function in ecstasy users: a study controlling for polydrug use.

RATIONALE: A number of studies have compared ecstasy users to control groups on various measures of neuropsychological function in order to determine whether ecstasy use results in lasting cognitive deficits. However, few of those studies controlled adequately for non-ecstasy illicit drug use. OBJECTIVE: The aim of this study was to investigate neuropsychological function in chronic ecstasy users while controlling for polydrug use. METHODS: Neuropsychological function was assessed in four groups-30 current 3,4-methylenedioxymethamphetamine (MDMA) users with a little history of illicit drug use other than ecstasy and cannabis, 30 polydrug controls, 30 drug-naïve controls and 20 ex-MDMA users-using a battery of well-validated, computerized neuropsychological tests. The battery focused on memory, executive function, impulsivity and risk-taking. RESULTS: Few differences were apparent between the groups, and on no measure were the current MDMA users impaired significantly relative to the polydrug controls. However, within the current MDMA users, questionnaire-measured impulsivity correlated with performance on a number of tests-a relationship that was not apparent in the controls. CONCLUSIONS: These data highlight the complexity in understanding the current ecstasy literature and suggest that some individuals may be particularly vulnerable to cognitive impairment following chronic use. Although no differences were identified between the current MDMA users and the controls, trait impulsiveness was significantly correlated with impairment on a number of neuropsychological outcome measures in the MDMA users, but not in the controls. These data suggest that impulsive individuals may be those most at risk for the development of cognitive impairment following chronic ecstasy use.

Amphetamine-Related Disorders↗
PubMed2005

Dissociating response selection and conflict in the medial frontal surface.

Response conflict and random response selection have both been associated with activations on the medial frontal surface. Random response selection was typically studied using a 'free selection' paradigm, in which subjects have to select between equally legitimate responses which are in competition with each other. Therefore, one interpretation is that the generation of spontaneous actions is merely a special case of the induction of response conflict. It has been reported that the generation of spontaneous actions is tightly associated with activity in the pre-supplementary motor area (pre-SMA). Most studies of response conflict, on the other hand, suggest that activations in a different and more ventral area, the anterior cingulate, reflect response conflict. Nonetheless, contradictory results have also been reported. To clarify this issue, in this experiment, we have put together a version of the Eriksen flanker task and a free selection task to allow for a direct comparison. We confirmed our hypothesis that free selection is associated with the pre-SMA, whereas response conflict is associated in the anterior cingulate. The two clusters of activation do not overlap, and the peaks of them were about 30 mm apart. We conclude that the activity in the pre-SMA is related to the endogenous generation of action rather than response conflict.

Adult↗
PubMed2005

Ventral striatum/nucleus accumbens activation to smoking-related pictorial cues in smokers and nonsmokers: a functional magnetic resonance imaging study.

BACKGROUND: Converging evidence from several theories of the development of incentive-sensitization to smoking-related environmental stimuli suggests that the ventral striatum plays an important role in the processing of smoking-related cue reactivity. METHODS: Twenty-six healthy right-handed volunteers (14 smokers and 12 nonsmoking controls) underwent functional magnetic resonance imaging (fMRI) during which neutral and smoking-related images were presented. Region of interest analyses were performed within the ventral striatum/nucleus accumbens (VS/NAc) for the contrast between smoking-related (SR) and nonsmoking related neutral (N) cues. RESULTS: Group activation for SR versus N cues was observed in smokers but not in nonsmokers in medial orbitofrontal cortex, superior frontal gyrus, anterior cingulate cortex, and posterior fusiform gyrus using whole-brain corrected Z thresholds and in the ventral VS/NAc using uncorrected Z-statistics (smokers Z = 3.2). Region of interest analysis of signal change within ventral VS/NAc demonstrated significantly greater activation to SR versus N cues in smokers than controls. CONCLUSIONS: This is the first demonstration of greater VS/NAc activation in addicted smokers than nonsmokers presented with smoking-related cues using fMRI. Smokers, but not controls, demonstrated activation to SR versus N cues in a distributed reward signaling network consistent with cue reactivity studies of other drugs of abuse.

Adult↗
PubMed2005

Executive function in Tourette's syndrome and obsessive-compulsive disorder.

BACKGROUND: Cognitive performance was compared in the genetically and neurobiologically related disorders of Tourette's syndrome (TS) and obsessive-compulsive disorder (OCD), in three domains of executive function: planning, decision-making and inhibitory response control. METHOD: Twenty TS patients, twenty OCD patients and a group of age- and IQ-matched normal controls completed psychometric and computerized cognitive tests and psychiatric rating scales. The cognitive tests were well-characterized in terms of their sensitivity to other fronto-striatal disorders, and included pattern and spatial recognition memory, attentional set-shifting, and a Go/No-go set-shifting task, planning, and decision-making. RESULTS: Compared to controls, OCD patients showed selective deficits in pattern recognition memory and slower responding in both pattern and spatial recognition, impaired extra-dimensional shifting on the set-shifting test and impaired reversal of response set on the Go/No-go test. In contrast, TS patients were impaired in spatial recognition memory, extra-dimensional set-shifting, and decision-making. Neither group was impaired in planning. Direct comparisons between the TS and OCD groups revealed significantly different greater deficits for recognition memory latency and Go/No-go reversal for the OCD group, and quality of decision-making for the TS group. CONCLUSIONS: TS and OCD show both differences (recognition memory, decision-making) and similarities (set-shifting) in selective profiles of cognitive function. Specific set-shifting deficits in the OCD group contrasted with their intact performance on other tests of executive function, such as planning and decision-making, and suggested only limited involvement of frontal lobe dysfunction, possibly consistent with OCD symptomatology.

Adult↗
PubMed2004

Distinct portions of anterior cingulate cortex and medial prefrontal cortex are activated by reward processing in separable phases of decision-making cognition.

BACKGROUND: Choosing between actions associated with uncertain rewards and punishments is mediated by neural circuitry encompassing the orbitofrontal cortex, anterior cingulate cortex (ACC), and striatum; however, the precise conditions under which these different components are activated during decision-making cognition remain uncertain. METHODS: Fourteen healthy volunteers completed an event-based functional magnetic resonance imaging protocol to investigate blood-oxygenation-level-dependent (BOLD) responses during independently modeled phases of choice cognition. In the "decision phase," participants decided which of two simultaneous visually presented gambles they wished to play for monetary reward. The gambles differed in their magnitude of gains, magnitude of losses, and the probabilities with which these outcomes were delivered. In the "outcome phase," the result of each choice was indicated on the visual display. RESULTS: In the decision phase, choices involving large gains were associated with increased BOLD responses in the pregenual ACC, paracingulate, and right posterior orbitolateral cortex compared with choices involving small gains. In the outcome phase, good outcomes were associated with increased BOLD responses in the posterior orbitomedial cortex, subcallosal ACC, and ventral striatum compared with negative outcomes. There was only limited overlap between reward-related activity in ACC and orbitofrontal cortex during the decision and outcome phases. CONCLUSIONS: Neural activity within the medial and lateral orbitofrontal cortex, pregenual ACC, and striatum mediate distinct representations of reward-related information that are deployed at different stages during a decision-making episode.

Adult↗
PubMed2004

Attention to intention.

Intention is central to the concept of voluntary action. Using functional magnetic resonance imaging, we compared conditions in which participants made self-paced actions and attended either to their intention to move or to the actual movement. When they attended to their intention rather than their movement, there was an enhancement of activity in the pre-supplementary motor area (pre-SMA). We also found activations in the right dorsal prefrontal cortex and left intraparietal cortex. Prefrontal activity, but not parietal activity, was more strongly coupled with activity in the pre-SMA. We conclude that activity in the pre-SMA reflects the representation of intention.

Attention↗
PubMed2003

Tryptophan depletion alters the decision-making of healthy volunteers through altered processing of reward cues.

While accumulating evidence suggests that effective real-life decision-making depends upon the functioning of the orbitofrontal cortex, much less is known about the involvement of the monoamine neurotransmitter systems and, in particular, serotonin. In the present study, we explored the impact of depleting the serotonin precursor, tryptophan, on human decision-making. Eighteen healthy volunteers consumed an amino-acid drink containing tryptophan and 18 healthy volunteers consumed an amino-acid drink without tryptophan, before choosing between simultaneously presented gambles, differing in the magnitude of expected gains (ie reward), the magnitude of expected losses (ie punishment), and the probabilities with which these outcomes were delivered. Volunteers also chose between gambles probing identified non-nomative biases in human decision-making, namely, risk-aversion when choosing between gains and risk-seeking when choosing between losses. Tryptophan-depleted volunteers showed reduced discrimination between magnitudes of expected gains associated with different choices. There was little evidence that tryptophan depletion was associated with altered discrimination between the magnitudes of expected losses, or altered discrimination between the relative probabilities with which these positive or negative outcomes were delivered. Risk-averse and risk-seeking biases were also unchanged. These results suggest that serotonin mediates decision-making in healthy volunteers by modulating the processing of reward cues, perhaps represented within the orbitofrontal cortex. It is possible that such a change in the cognition mediating human choice is one mechanism associated with the onset and maintenance of anhedonia and lowered mood in psychiatric illness.

Adult↗