Rapid visuomotor preparation in the human brain: a functional MRI study

Age-related decline of online visuomotor adaptation: a combined effect of deteriorations of motor anticipation and execution

The literature has established that the capability of visuomotor adaptation decreases with aging. However, the underlying mechanisms of this decline are yet to be fully understood. The current study addressed this issue by examining how aging affected visuomotor adaptation in a continuous manual tracking task with delayed visual feedback. To distinguish separate contributions of the declined capability of motor anticipation and deterioration of motor execution to this age-related decline, we recorded and analyzed participants' manual tracking performances and their eye movements during tracking. Twenty-nine older people and twenty-three young adults (control group) participated in this experiment. The results showed that the age-related decline of visuomotor adaptation was strongly linked to degraded performance in predictive pursuit eye movement, indicating that declined capability motor anticipation with aging had critical influences on the age-related decline of visuomotor adaptation. Additionally, deterioration of motor execution, measured by random error after controlling for the lag between target and cursor, was found to have an independent contribution to the decline of visuomotor adaptation. Taking these findings together, we see a picture that the age-related decline of visuomotor adaptation is a joint effect of the declined capability of motor anticipation and the deterioration of motor execution with aging.

Explaining the neural activity distribution associated with discrete movement sequences: Evidence for parallel functional systems

To explore the effects of practice we scanned participants with fMRI while they were performing four-key unfamiliar and familiar sequences, and compared the associated activities relative to simple control sequences. On the basis of a recent cognitive model of sequential motor behavior (C-SMB), we propose that the observed neural activity would be associated with three functional networks that can operate in parallel and that allow (a) responding to stimuli in a reaction mode, (b) sequence execution using spatial sequence representations in a central-symbolic mode, and (c) sequence execution using motor chunk representations in a chunking mode. On the basis of this model and findings in the literature, we predicted which neural areas would be active during execution of the unfamiliar and familiar keying sequences. The observed neural activities were largely in line with our predictions, and allowed functions to be attributed to the active brain areas that fit the three above functional systems. The results corroborate C-SMB’s assumption that at advanced skill levels the systems executing motor chunks and translating key-specific stimuli are racing to trigger individual responses. They further support recent behavioral indications that spatial sequence representations continue to be used.

The Primary Motor and Premotor Areas of the Human Cerebral Cortex

Brodmann's cytoarchitectonic map of the human cortex designates area 4 as cortex in the anterior bank of the precentral sulcus and area 6 as cortex encompassing the precentral gyrus and the posterior portion of the superior frontal gyrus on both the lateral and medial surfaces of the brain. More than 70 years ago, Fulton proposed a functional distinction between these two areas, coining the terms primary motor areafor cortex in Brodmann area 4 and premotor areafor cortex in Brodmann area 6. The parcellation of the cortical motor system has subsequently become more complex. Several nonprimary motor areas have been identified in the brain of the macaque monkey, and associations between anatomy and function in the human brain are being tested continuously using brain mapping techniques. In the present review, the authors discuss the unique properties of the primary motor area (M1), the dorsal portion of the premotor cortex (PMd), and the ventral portion of the premotor cortex (PMv). They end this review by discussing how the premotor areas influence M1.

The stuff that motor chunks are made of: Spatial instead of motor representations?

In order to determine how participants represent practiced, discrete keying sequences in the discrete sequence production task, we had 24 participants practice two six-key sequences on the basis of two pre-learned six-digit numbers. These sequences were carried out by fingers of the left (L) and right (R) hand with between-hand transitions always occurring between the second and third, and the fifth and sixth responses. This yielded the so-called LLRRRL and RRLLLR sequences. Early and late in practice, the keypad used for the right hand was briefly relocated from the front of the participants to 90° at their right side. The results indicate that after 600 practice trials, executing a keying sequence relies heavily on a spatial cross-hand representation in a trunk- or head-based reference frame that after about only 15 trials is fully adjusted to the changed hand location. The hand location effect was not found with the last sequence element. This is attributed to the application of explicit knowledge. The between-hand transitions appeared to induce initial segmentation in some of the participants, but this did not consolidate into a concatenation point of successive motor chunks.

The burden and predictors of cognitive impairment among 6- to 8-year-old children infected and uninfected with HIV from Harare, Zimbabwe: a cross-sectional study

With long-term survival of children infected with HIV, information on cognitive function at school age is needed. To determine cognitive function among 6- to 8 year-old children exposed to HIV and to assess factors associated with cognitive impairment, we conducted a cross-sectional study from October 2010 to December 2011 among children whose mothers participated in a national HIV prevention program in Harare. Cognitive function was assessed using the McCarthy Scales of Children's Abilities (MSCA). Of the 306 assessed children, 32 (10%) were HIV infected, 121 (40%) exposed uninfected, and 153 (50%) unexposed uninfected. The mean (SD) General Cognitive Index for the whole study group was 82 (15). An overall of 49 (16%) out of the 306 children had cognitive impairment with no difference in general cognitive function among the three groups. Children with HIV infection scored lowest in perceptual performance domain, p = .028. Unemployed caregivers, child orphanhood and undernutrition were associated with impaired cognitive performance in univariate analysis. In multivariate analysis, caregiver unemployment status remained a factor associated with cognitive impairment with an ODDS ratio of 2.1 (95% CI 1.03-3.36). In a cohort of 6- to 8-year-olds, HIV infection did not show evidence of significant difference in general cognitive function. Children infected with HIV had major deficits in perceptive performance. Lower socioeconomic status was associated with cognitive impairment. In resource-constrained settings, strategies aimed at poverty alleviation and good nutritional management should complement early infant diagnosis and treatment of HIV in order to optimize neurocognitive potential.

Effect of predictive cuing on response inhibition in children with heavy prenatal alcohol exposure

BACKGROUND

Heavy prenatal exposure to alcohol leads to widespread cognitive deficits, including problems with attention and response inhibition. This study examined blood oxygen level-dependent response in children with and without histories of heavy prenatal alcohol exposure during a task of response inhibition consisting of cued and noncued trials.

METHODS

Children and adolescents (ages 8 to 18 years) with (alcohol-exposed [AE] = 20) and without (control [CON] = 15) histories of heavy prenatal exposure to alcohol underwent functional magnetic resonance imaging while performing a go/no-go task. Unbeknownst to subjects, a predictive cue preceded the no-go stimulus in 87% of trials.

RESULTS

Groups were matched on demographic variables and did not differ on most measures of task performance. However, following cued stimuli, the AE group demonstrated a lower hit rate to go stimuli and more conservative response bias than the CON group. AE participants demonstrated more activation during no-go trials (inhibition) relative to go trials in the left precuneus, cingulate gyrus, anterior cingulate, and right medial frontal gyrus. During cue-dependent response inhibition, the AE group demonstrated less activation in the left precentral and postcentral gyrus compared to the CON group.

CONCLUSIONS

Consistent with previous studies of response inhibition, the AE group demonstrated greater frontal and parietal activation when attempting to inhibit prepotent responses than the CON group, despite similar rates of commission errors. This study further demonstrated that the AE group had impaired behavioral performance on cued trials and demonstrated less activation in precentral and postcentral gyri relative to the CON group on these trials. This investigation provides evidence of impaired behavioral and neural processing of sequential information in fetal alcohol spectrum disorders, which can help improve inhibition in typical populations.

Grouping mechanisms in response preparation investigated with event-related brain potentials

Preliminary information about responses facilitates performance, especially when the information can be grouped into stimulus-response sets, for example, into fingers belonging to the same hand. Here, we studied the mechanisms of supposedly fast and automatic exogenous as compared to slow and controlled endogenous grouping of same-hand fingers. As compared to endogenous cuing, exogenous cuing facilitated reaction times and induced larger amplitudes of the contingent negative variation, but did not show any advantage in amplitude or latency of the lateralized readiness potential or in the magnitude of current source density over the motor cortices. Similarly, the stimulus preceding negativity did not seem to be a plausible explanation for the observed effect. Therefore, at least one functional mechanism underlying exogenous stimulus-response grouping appears to be the facilitation of central response programming.

Spared within-hands but impaired between-hands response preparation in aging

OBJECTIVES

Older people can use advance information to prepare a subset of finger responses. It is debated, however, whether aging affects the preparation of finger responses on two hands (between-hands preparation) more strongly than the preparation of finger responses on one hand (within-hands preparation). The present study examined the role of temporal uncertainty in this issue.

METHODS

We asked a group of young and older participants to perform a finger-cuing task with four preparation intervals (2, 3, 4, and 5 s), presented either separately in distinct blocks of trials (fixed design: no temporal uncertainty) or randomly intermixed across trials (mixed design: temporal uncertainty).

RESULTS

Reaction time and error rates revealed age equivalence for within-hands preparation but an age-related difference for between-hands preparation, regardless of how the preparation intervals were presented.

DISCUSSION

These findings demonstrate a robust, structural difference in the maximal preparation benefit that older adults can achieve when preparing two fingers on two hands but not on one hand. These outcomes are discussed in terms of several theories of cognitive aging.

The role of response modalities in cognitive task representations

The execution of a task necessitates the use of a specific response modality. We examined the role of different response modalities by using a task-switching paradigm. In Experiment 1, subjects switched between two numerical judgments, whereas response modality (vocal vs. manual vs. foot responses) was manipulated between groups. We found judgment-shift costs in each group, that is irrespective of the response modality. In Experiment 2, subjects switched between response modalities (vocal vs. manual, vocal vs. foot, or manual vs. foot). We observed response-modality shift costs that were comparable in all groups. In sum, the experiments suggest that the response modality (combination) does not affect switching per se. Yet, modality-shift costs occur when subjects switch between response modalities. Thus, we suppose that modality-shift costs are not due to a purely motor-related mechanisms but rather emerge from a general switching process. Consequently, the response modality has to be considered as a cognitive component in models of task switching.

Response preparation with static and moving hands: differential effects of unimanual and bimanual movements

This study investigated the effects of uni- and bimanual hand movements on the efficiency of within- and between-hands response preparation in a spatial cuing task. Predictions were derived from the Grouping Model of finger preparation, inspired by insights from neurophysiology (i.e., the concepts of transcollosal facilitation and cognitive overruling of basic neural coordination patterns). Sixteen participants performed the finger cuing task with one, two, or no hand(s) moving. Reaction time results revealed that unimanual and bimanual hand movements had similar effects on within-hand preparation but differential effects on between-hands preparation. This finding demonstrates a strong dissociation between within- and across-hands finger preparation, suggesting distinct underlying mechanisms as hypothesized by the Grouping Model.

Cue validity effects in response preparation: a pupillometric study

This study examined the effects of cue validity and cue difficulty on response preparation to provide a test of the Grouping Model [Adam, J.J., Hommel, B. and Umiltà, C., 2003. Preparing for perception and action (I): the role of grouping in the response-cuing paradigm. Cognit. Psychol. 46(3), 302-58, Adam, J.J., Hommel, B. and Umiltà, C., 2005. Preparing for perception and action (II) automatic and effortful processes in response cuing. Vis. Cogn. 12(8), 1444-1473.]. We used the pupillary response to index the cognitive processing load during and after the preparatory interval (2 s). Twenty-two participants performed the finger-cuing tasks with valid (75%) and invalid (25%) cues. Results showed longer reaction times, more errors, and larger pupil dilations for invalid than valid cues. During the preparation interval, pupil dilation varied systematically with cue difficulty, with easy cues (specifying 2 fingers on 1 hand) showing less pupil dilation than difficult cues (specifying 2 fingers on 2 hands). After the preparation interval, this pattern of differential pupil dilation as a function of cue difficulty reversed for invalid cues, suggesting that cues which incorrectly specified fingers on one hand required more effortful reprogramming operations than cues which incorrectly specified fingers on two hands. These outcomes were consistent with predictions derived from the Grouping Model. Finally, all participants exhibited two distinct pupil dilation strategies: an "early" strategy in which the onset of the main pupil dilation was tied to onset of the cue, and a "late" strategy in which the onset of the main pupil dilation was tied to the onset of the target. Thus, whereas the early pupil dilation strategy showed a strong dilation during the preparation interval, the late pupil strategy showed a strong constriction. Interestingly, only the late onset pupil dilation strategy revealed the above reported sensitivity to cue difficulty, showing for the first time that the well-known pupil's sensitivity to task difficulty can also emerge when the pupil is constricting instead of dilating.

Modifying the Cortical Processing for Motor Preparation by Repetitive Transcranial Magnetic Stimulation

To investigate the effects of repetitive transcranial magnetic stimulation (rTMS) on the central processing of motor preparation, we had subjects perform a precued-choice reaction time (RT) task. They had to press one of two buttons as quickly as possible after a go signal specifying both the hand to be used and the button to press. A precue preceding this signal conveyed full, partial, or no advance information (hand and/or button), such that RT shortened with increasing amount of information. We applied 1200 to 2400 pulses of 1-Hz rTMS over various cortical areas and compared the subjects' performances at various times before and after this intervention. rTMS delayed RT at two distinct phases after stimulation, one within 10 min and another with a peak at 20 to 30 min and lasting for 60 to 90 min, with no significant effects on error rates or movement time. The effect was significantly larger on left- than on right-hand responses. RT was prominently delayed over the premotor and motor cortices with similar effects across different conditions of advance information, suggesting that preparatory processes relatively close to the formation of motor output were influenced by rTMS. In contrast, the effect of rTMS over the supplementary motor area and the anterior parietal cortex varied with the amount of advance information, indicating specific roles played by these areas in integrating target and effector information. The primary motor area, especially of the left hemisphere, may take over this processing, implementing motor output based on the information processed in other areas.

Response preparation with static versus moving hands

This research tested the response inhibition account of the hand-advantage found in the finger pre-cuing task. According to this account, the advantage of preparing two fingers on one hand (represented in one hemisphere) as opposed to preparing two fingers on two hands (represented in two hemispheres) is due, in part, to a response inhibition process that operates more efficiently within than between hemispheres. In this view, supplying extra activation to both hemispheres by moving the hands should decrease the within-hemisphere inhibition advantage. Twelve participants performed the finger pre-cuing task with static and moving hands. As predicted by the response inhibition account, the hand-advantage, present with the hands at rest, decreased with the hands moving.

Neural changes in control implementation of a continuous task

It is commonly agreed that control implementation, being a resource-consuming endeavor, is not exerted continuously or in simple tasks. However, most research in the field was done using tasks that varied the need for control on a trial-by-trial basis (e.g., Stroop, flanker) in a discrete manner. In this case, the anterior cingulate cortex (ACC) was found to monitor the need for control, whereas regions in the prefrontal cortex (PFC) were found to be involved in control implementation. Whether or not the same control mechanism would be used in continuous tasks was an open question. In our study, we found that in a continuous task, the same neural substrate subserves control monitoring (ACC) but that the neural substrate of control implementation changes over time. Early in the task, regions in the PFC were involved in control implementation, whereas later the control was taken over by subcortical structures, specifically the caudate. Our results suggest that humans possess a flexible control mechanism, with a specific structure dedicated to monitoring the need for control and with multiple structures involved in control implementation.

Individuals with schizophrenia present hypo- and hyperactivation during implicit cueing in an inhibitory task

BACKGROUND

The primary purpose of this investigation was to assess the neural correlates of implicit cueing during an inhibitory task in schizophrenia when performance accuracy was matched with healthy comparison subjects.

METHODS

We compared 17 individuals with chronic schizophrenia (SZ; medicated, 13.9 average years of illness) and 17 healthy comparison subjects (HC) matched for hit and false alarm rates, age, and education on a visual Go/Nogo task during functional magnetic resonance imaging. In this task, one of the go stimuli also served implicitly as a cue predictive of a subsequent inhibitory (Nogo) trial.

CONCLUSIONS

Findings suggest that even when matched for overall performance accuracy, individuals with SZ exhibit difficulties with inhibition and cue processing that may relate to core deficits in cognitive control and stimulus processing. In particular, these findings point towards an important role of the parietal cortex for cued inhibitory processes in healthy populations.

Neural correlate of spatial presence in an arousing and noninteractive virtual reality: an EEG and psychophysiology study

Using electroencephalography (EEG), psychophysiology, and psychometric measures, this is the first study which investigated the neurophysiological underpinnings of spatial presence. Spatial presence is considered a sense of being physically situated within a spatial environment portrayed by a medium (e.g., television, virtual reality). Twelve healthy children and 11 healthy adolescents were watching different virtual roller coaster scenarios. During a control session, the roller coaster cab drove through a horizontal roundabout track. The following realistic roller coaster rides consisted of spectacular ups, downs, and loops. Low-resolution brain electromagnetic tomography (LORETA) and event-related desynchronization (ERD) were used to analyze the EEG data. As expected, we found that, compared to the control condition, experiencing a virtual roller coaster ride evoked in both groups strong SP experiences, increased electrodermal reactions, and activations in parietal brain areas known to be involved in spatial navigation. In addition, brain areas that receive homeostatic afferents from somatic and visceral sensations of the body were strongly activated. Most interesting, children (as compared to adolescents) reported higher spatial presence experiences and demonstrated a different frontal activation pattern. While adolescents showed increased activation in prefrontal areas known to be involved in the control of executive functions, children demonstrated a decreased activity in these brain regions. Interestingly, recent neuroanatomical and neurophysiological studies have shown that the frontal brain continues to develop to adult status well into adolescence. Thus, the result of our study implies that the increased spatial presence experience in children may result from the not fully developed control functions of the frontal cortex.

Effects of thirty-minute mobile phone use on visuo-motor reaction time

OBJECTIVE

To investigate whether exposure to pulsed high-frequency electromagnetic field (pulsed EMF) emitted by a mobile phone has short-term effects on the visuo-motor choice reaction time (RT) and movement time (MT).

METHODS

A double blind, counterbalanced crossover design was employed. In 16 normal subjects, we studied the performance of a visuo-motor precued choice reaction time task (PCRT) before and after exposure to EMF emitted by a mobile phone for 30 minutes or sham exposure.

RESULTS

The RTs and MTs under different conditions of precue information were not affected by exposure to pulsed EMF emitted by a mobile phone or by sham phone use.

CONCLUSIONS

Thirty minutes of mobile phone use has no significant short-term effect on the cortical visuo-motor processing as studied by the present PCRT task.

SIGNIFICANCE

This is the first study to investigate visuo-motor behavior in relation to mobile phone exposure. No significant effect of mobile phone use was demonstrated on the performance of the visuo-motor reaction time task.

Three-dimensional locations and boundaries of motor and premotor cortices as defined by functional brain imaging: a meta-analysis

The mesial premotor cortex (pre-supplementary motor area and supplementary motor area proper), lateral premotor cortex (dorsal premotor cortex and ventral premotor cortex), and primary sensorimotor cortex (primary motor cortex and primary somatosensory cortex) have been identified as key cortical areas for sensorimotor function. However, the three-dimensional (3-D) anatomic boundaries between these regions remain unclear. In order to clarify the locations and boundaries for these six sensorimotor regions, we surveyed 126 articles describing pre-supplementary motor area, supplementary motor area proper, dorsal premotor cortex, ventral premotor cortex, primary motor cortex, and primary somatosensory cortex. Using strict inclusion criteria, we recorded the reported normalized stereotaxic coordinates (Talairach and Tournoux or MNI) from each experiment. We then computed the probability distributions describing the likelihood of activation, and characterized the shape, extent, and area of each sensorimotor region in 3-D. Additionally, we evaluated the nature of the overlap between the six sensorimotor regions. Using the findings from this meta-analysis, along with suggestions and guidelines of previous researchers, we developed the Human Motor Area Template (HMAT) that can be used for ROI analysis. HMAT is available through e-mail from the corresponding author.

Parallel networks operating across attentional deployment and motion processing: a multi-seed partial least squares fMRI study

Anticipatory deployment of attention may operate through networks of brain areas that modulate the representations of to-be-attended items in advance of their occurrence through top-down control. Luks and Simpson (2004) (Luks, T.L., Simpson, G.V., 2004. Preparatory deployment of attention to motion activates higher order motion-processing brain regions. NeuroImage 22, 1515-1522) found activations in both control areas and sensory areas during anticipatory deployment of attention to visual motion in the absence of stimuli. In the present follow-up analysis, we tested which network activity during anticipatory deployment of attention is functionally connected with task-related network activity during subsequent selective processing of motion stimuli. Following a cue (anticipatory phase), participants monitored a sequence of complex motion stimuli for a target motion pattern (task phase). We analyzed fMR signal using a partial least squares analysis with previously identified cue- and motion-related voxels as seed regions. The method identified two networks that covaried with the activity of seed regions during the cue and motion-stimulus-processing phases of the task. We suggest that the first network, involving ventral intraparietal sulcus, superior parietal lobule and motor areas, is related to anticipatory and sustained visuomotor attention. Operating in parallel to this visuomotor attention network, there is a second network, involving visual occipital areas, frontal areas as well as angular and supramarginal gyri, that may underlie anticipatory and sustained visual attention processes.

Neural correlates of dual-task performance after minimizing task-preparation

Previous dual-task neuroimaging studies have not discriminated between brain regions involved in preparing to make more than one response from those involved in the management and execution of two tasks. To isolate the effects of dual-task processing while minimizing effects related to task-preparatory processes, we employed a blocked event-related design in which single trials and dual trials were randomly and unpredictably intermixed for one block (mixed block) and presented in isolation of one another during other blocks (pure blocks). Any differences between dual-task and single-task trials within the mixed block would be related to dual-task performance while minimizing any effects related to preparatory differences between the conditions. For this comparison, we found dual-task-related activation throughout inferior prefrontal, temporal, extrastriate, and parietal cortices and the basal ganglia. In addition, when comparing the single task within the mixed block with the single task presented in the pure block of trials, the regions involved in processes important in the mixed block yet unrelated to dual-task operations could be specified. In this comparison, we report a pattern of activation in right inferior prefrontal and superior parietal cortices. Our results argue that a variety of neural regions remain active during dual-task performance even after minimizing task-preparatory processes, but some regions implicated in dual-task performance in previous studies may have been due to task-preparation processes. Furthermore, our results suggest that dual-task operations activate the same brain areas as the single tasks, but to a greater magnitude than the single tasks. These results are discussed in relation to current conceptions of the neural correlates of dual-task performance.

Preparation for speeded action as a psychophysiological concept

Mental preparation aids performance and induces multiple physiological changes that should inform concepts of preparation. To date, however, these changes have been interpreted as being due to a global preparatory process (e.g., attention or alertness). The authors review psychophysiological and performance investigations of preparation. Concepts of the central regulation of action offer an integrative framework for understanding the psychophysiology of preparation. If people process multiple streams of information concurrently, then preparatory processing requires a form of supervisory attention- central regulation to maintain unity of action. This concept is consistent with existing psychophysiological results and links them to current views of information processing. Conversely, psychophysiological measures may provide indices to test concepts within theories of the central regulation of action.

Controlled visuomotor preparation deficits in attention-deficit/hyperactivity disorder

To the best of the authors' knowledge, there are no published reports on visuomotor preparation in attention-deficit/hyperactivity disorder (ADHD). This is unfortunate, because research suggests that ADHD is an output-related deficit, and suboptimal execution of tasks may be the result of incomplete visuomotor preparation. The authors compared 19 children with ADHD with 124 healthy and 120 pathological controls in terms of their performance (speed, speed variability, and accuracy) on the finger precuing test, a test measuring (automatic and controlled) visuomotor preparation. The data implied that children with ADHD have an impaired ability to engage in effortful, controlled visuomotor preparation activities. Fast, automatic response preparation was not affected by ADHD. In addition, children with ADHD showed more variability in overall test performance than other children. No group differences were found in response accuracy.

Interhemispheric Transmission of Visuomotor Information for Motor Implementation

Using transcranial magnetic stimulation (TMS), we addressed the contribution of both hemispheres to the visuomotor control of each hand. The subjects had to press one of two buttons as quickly as possible after the go-signal. A precue preceding this conveyed full, partial or no advance information (hand and/or button), such that reaction time (RT) shortened with increasing amount of information. We gave TMS over each hemisphere at various time intervals (100-350 ms) after the go-signal and before the expected onset of response, and measured its effect on RT, movement time (MT) and error rate. At short intervals (100-200 ms), left hemisphere TMS delayed RT and prolonged MT of both hands, while right hemisphere TMS delayed RT only of the right hand, without affecting error rates. At long intervals (250-350 ms), TMS produced slightly more pronounced RT delays of the contralateral hand. RT was delayed more if the precues were less informative. The results suggest the importance of interhemispheric transmission of visuomotor information for motor implementation. The right hemisphere may play a role mainly in calculating target and effector information, determining RT, while the left hemisphere may play a role in elaborating the motor program and determining MT.

Direct activation of the ventral striatum in anticipation of aversive stimuli

The brain "reward" system, centered on the limbic ventral striatum, plays a critical role in the response to pleasure and pain. The ventral striatum is activated in animal and human studies during anticipation of appetitive/pleasurable events, but its role in aversive/painful events is less clear. Here we present data from three human fMRI studies based on aversive conditioning using unpleasant cutaneous electrical stimulation and show that the ventral striatum is reliably activated. This activation is observed during anticipation and is not a consequence of relief after the aversive event. Further, the ventral striatum is activated in anticipation regardless of whether there is an opportunity to avoid the aversive stimulus or not. Our data suggest that the ventral striatum, a crucial element of the brain "reward" system, is directly activated in anticipation of aversive stimuli.

Preparing for perception and action (I): the role of grouping in the response-cuing paradigm

Human skilled behavior requires preparatory processes that selectively make sensory and motor systems more efficient for perceiving the upcoming stimulus and performing the correct action. We review the literature concerning these preparatory processes as studied by response-cuing paradigm, and propose a model that accounts for the major findings. According to the Grouping Model, advance or precue information directs a dynamic process of subgroup making-that is, a process of stimulus- and response-set reconfiguration-whereby the internal representation of the task is simplified. The Grouping Model assigns a critical role to the unit of selection, with Gestalt factors and interresponse dependencies mediating the formation and strength of stimulus and response subgroups. In a series of five experiments, we manipulated perceptual and motoric grouping factors, and studied their independent and interactive effects on the pattern of precuing benefits. Generally, the results were consistent with the Grouping Model's account of response-cuing effects.