Signal-, set- and movement-related activity in the human brain: an event-related fMRI study.
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Electrophysiological studies on monkeys have been able to distinguish sensory and motor signals close in time by pseudorandomly delaying the cue that instructs the movement from the stimulus that triggers the movement. We have used a similar experimental design in functional magnetic resonance imaging (fMRI), scanning subjects while they performed a visuomotor conditional task with instructed delays. One of four shapes was presented briefly. Two shapes instructed the subjects to flex the index finger; the other two shapes coded the flexion of the middle finger. The subjects were told to perform the movement after a tone. We have exploited a novel use of event-related fMRI. By systematically varying the interval between the visual and acoustic stimuli, it has been possible to estimate the significance of the evoked haemodynamic response (EHR) to each of the stimuli, despite their temporal proximity in relation to the time constant of the EHR. Furthermore, by varying the phase between events and image acquisition, we have been able to achieve high temporal resolution while scanning the whole brain. We dissociated sensory and motor components of the sensorimotor transformations elicited by the task, and assessed sustained activity during the instructed delays. In calcarine and occipitotemporal cortex, the responses were exclusively associated with the visual instruction cues. In temporal auditory cortex and in primary motor cortex, they were exclusively associated with the auditory trigger stimulus. In ventral prefrontal cortex there were movement-related responses preceded by preparatory activity and by signal-related activity. Finally, responses associated with the instruction cue and with sustained activity during the delay period were observed in the dorsal premotor cortex and in the dorsal posterior parietal cortex. Where the association between a visual cue and the appropriate movement is arbitrary, the underlying visuomotor transformations are not achieved exclusively through frontoparietal interactions. Rather, these processes seem to rely on the ventral visual stream, the ventral prefrontal cortex and the anterior part of the dorsal premotor cortex. (+info)
Neural encoding in orbitofrontal cortex and basolateral amygdala during olfactory discrimination learning.
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Orbitofrontal cortex (OFC) is part of a network of structures involved in adaptive behavior and decision making. Interconnections between OFC and basolateral amygdala (ABL) may be critical for encoding the motivational significance of stimuli used to guide behavior. Indeed, much research indicates that neurons in OFC and ABL fire selectively to cues based on their associative significance. In the current study recordings were made in each region within a behavioral paradigm that allowed comparison of the development of associative encoding over the course of learning. In each recording session, rats were presented with novel odors that were informative about the outcome of making a response and had to learn to withhold a response after sampling an odor that signaled a negative outcome. In some cases, reversal training was performed in the same session as the initial learning. Ninety-six of the 328 neurons recorded in OFC and 60 of the 229 neurons recorded in ABL exhibited selective activity during evaluation of the odor cues after learning had occurred. A substantial proportion of those neurons in ABL developed selective activity very early in training, and many reversed selectivity rapidly after reversal. In contrast, those neurons in OFC rarely exhibited selective activity during odor evaluation before the rats reached the criterion for learning, and far fewer reversed selectivity after reversal. The findings support a model in which ABL encodes the motivational significance of cues and OFC uses this information in the selection and execution of an appropriate behavioral strategy. (+info)
Visual control of locomotion in Parkinson's disease.
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The effect of placing parallel lines on the walking surface on parkinsonian gait was evaluated. To identify the kind of visual cues (static or dynamic) required for the control of locomotion, we tested two visual conditions: normal lighting and stroboscopic illumination (three flashes/s), the latter acting to suppress dynamic visual cues completely. Sixteen subjects with idiopathic Parkinson's disease (nine males, seven females; mean age 68.8 years) and the same number of age-matched controls (seven males; nine females, mean age 67.5 years) were studied. During the baseline phase, Parkinson's disease patients walked with a short-stepped, slow velocity pattern. The double limb support duration was increased and the step cadence was reduced relative to normal. Under normal lighting, visual cues from the lines on the walking surface induced a significant improvement in gait velocity and stride length in Parkinson's disease patients. With stroboscopic illumination and without lines, both groups reduced their stride length and velocity but the changes were significant only in the Parkinson's disease group, indicating greater dependence on dynamic visual information. When stroboscopic light was used with stripes on the floor, the improvement in gait due to the stripes was suppressed in parkinsonian patients. These results demonstrate that the perceived motion of stripes, induced by the patient's walking, is essential to improve the gait parameters and thus favour the hypothesis of a specific visual-motor pathway which is particularly responsive to rapidly moving targets. Previous studies have proposed a cerebellar circuit, allowing the visual stimuli to by-pass the damaged basal ganglia. (+info)
A nicotine antagonist, mecamylamine, reduces cue-induced cocaine craving in cocaine-dependent subjects.
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We have previously shown that nicotine enhances cue-induced cocaine craving. In the present study, the effects of a nicotine antagonist, mecamylamine, on cue-induced cocaine craving were investigated. Twenty-three cocaine-dependent patients, all cigarette smokers, were randomly assigned to mecamylamine (2.5 mg tablet) or placebo in a single-dose, placebo-controlled, crossover, double-blind study. Craving and anxiety were measured before and after cocaine cues with visual analog scales for desire to use cocaine and mood. Skin conductance, skin temperature and heart rate were recorded before and during cocaine cues. Following exposure to cocaine cues, all patients reported an increase in cocaine craving and anxiety relative to the precue measures. Cue exposure also produced an increase in skin conductance and decrease in skin temperature. The cue-induced increase in cocaine craving was reduced, while the cue-induced skin conductance and temperature responses were unaffected, by mecamylamine. These findings show that cue-induced cocaine craving is attenuated by mecamylamine. Further study on the use of mecamylamine in relapse prevention programs are suggested. (+info)
Auditory perception: does practice make perfect?
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Recent studies have shown that adult humans can learn to localize sounds relatively accurately when provided with altered localization cues. These experiments provide further evidence for experience-dependent plasticity in the mature brain. (+info)
Effect of number of home exercises on compliance and performance in adults over 65 years of age.
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BACKGROUND AND PURPOSE: There is limited research on the effects of the number of exercises a person is told to perform on compliance and performance, as defined by cueing requirements, correct alignment, and quality of movement. Some studies of medication suggest that compliance decreases as the number of medications increases. The purpose of this study was to determine whether older adults comply and perform better (ie, requiring less cueing, exhibiting correct alignment, and exhibiting controlled, coordinated, and continuous movements) when they are asked to do 2, 5, or 8 exercises. SUBJECTS: Subjects were 11 women and 4 men, aged 67 to 82 years (X=72.8), who were living independently in their communities. METHODS: Subjects were randomly prescribed 2, 5, or 8 general strengthening home exercises. They were instructed on their exercises at an initial session and asked to record the number of repetitions performed each day in a self-report exercise log. At a return session 7 to 10 days later, subjects were scored on their performance of the prescribed exercises using a newly designed assessment tool. RESULTS: The group that was prescribed 2 exercises performed better, as defined by their performance tool score, than the group that was prescribed 8 exercises. The group that was prescribed 5 exercises was not different from the groups that performed 2 or 8 exercises. No differences were found among groups regarding the self-report measurement of compliance. There was a moderate correlation between performance scores and the self-report percentage rates. CONCLUSION AND DISCUSSION: Subjects who were prescribed 2 exercises performed better than subjects who were prescribed 8 exercises. The question of an optimal number of exercises to prescribe to elderly people warrants further study. (+info)
Parallel information processing in the dorsal striatum: relation to hippocampal function.
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We investigated the effects of localized medial and lateral CPu lesions and fornix/fimbria lesions on responses to a local cue and to behavior based on cognitive-spatial information in the water maze. Rats were trained concurrently on the cue (visible platform) and spatial (submerged platform) components of the task, followed by a test in which responses to the two types of information were dissociated by a measure of competing response tendencies. Bilateral lesions of lateral CPu did not affect acquisition of either cue or spatial responding but produced a preference for the spatial response on the competition test. Bilateral lesions of the medial CPu retarded but did not prevent learning both components and produced a preference for the cue response on the competition test. The latter effect was accompanied by increased thigmotaxis (swimming in the periphery of the pool), primarily during the early acquisition trials, which was attributed to an impaired ability to respond to learned spatial information. Fornix/fimbria lesions prevented spatial but not cue learning and produced a preference for the cue response on the competition test. Asymmetric lesions (unilateral hippocampus and contralateral medial CPu) produced mild retardation of acquisition of both the cue and spatial tasks and a preference for the cue response on the competition test. These findings dissociate the functions of the lateral and medial CPu and suggest that the hippocampus and medial CPu may be parts of a system that promotes responding based on learned cognitive-spatial information, particularly in competitive cue-place response situations. (+info)
Impairment of willed actions and use of advance information for movement preparation in schizophrenia.
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OBJECTIVES: To assess willed actions in patients with schizophrenia using reaction time (RT) tasks that differ in the degree to which they involve volitionally controlled versus stimulus driven responses. METHODS: Ten patients diagnosed with schizophrenia and 13 normal controls of comparable age were tested. Subjects performed a visual simple RT (SRT), an uncued four choice reaction time (CRT), and a fully cued four choice RT task. A stimulus 1(S1)-stimulus 2(S2) paradigm was used. The warning signal/precue (S1) preceded the imperative stimulus (S2) by either 0 (no warning signal or precue) 200, 800, 1600, or 3200 ms. RESULTS: The patients with schizophrenia had significantly slower RTs and movement times than normal subjects across all RT tasks. The unwarned SRT trials were significantly faster than the uncued CRT trials for both groups. For both groups, fully cued CRTs were significantly faster than the uncued CRTs. However, the S1-S2 interval had a differential effect on CRTs in the two groups. For the normal subjects fully cued CRTs and SRTs were equivalent when S1-S2 intervals were 800 ms or longer. A similar pattern of effects was not seen in the patients with schizophrenia, for whom the fully cued CRT were unexpectedly equivalent to SRT for the 200 ms interval and expectedly for the 1600 ms S1-S2 interval, but not the 3200 or 800 ms intervals. CONCLUSIONS: Patients with schizophrenia were able to use advance information inherent in SRT or provided by the precue in fully cued CRT to speed up RT relative to uncued CRT. However, in the latter task, in which the volitional demands of preprogramming are higher since a different response has to be prepared on each trial, patients showed some unusual and inconsistent interval effects suggesting instability of attentional set. It is possible that future studies using RT tasks with higher volitional demands in patients with predominance of negative signs may disclose greater deficits in willed action in schizophrenia. (+info)