Biomedical subjects

Sean C Hinton

Publications and source records attributed to Sean C Hinton.

4 recordsLinked to original sources

PubMed2004

Neural systems supporting timing and chronometric counting: an FMRI study.

At least two strategies are available to humans for estimating multisecond intervals. One depends on an interval timing system that is common to many species. The other is the language-based strategy of chronometric counting. These two strategies are easily distinguished by the psychophysical properties of their behavioral correlates: counting supports substantially more precise estimates than are possible using the more general interval timing system. The present study investigates the neural systems that underlie the execution of these different strategies. Eighteen adults reproduced a 16-s interval either by internally timing or covertly counting the duration. Comparison of counting and timing to a resting baseline suggested that these strategies engage some nonoverlapping neural systems. Counting, but not timing, strongly activated Broca's area, primary motor cortex in the mouth region, and right cerebellum, all of which are associated with internal speech. Counting also activated parts of the medial premotor circuit, including the putamen, supplementary motor area (SMA) proper, and cingulate motor area (CMA), that have been associated with reproducing isochronous and syncopated rhythms of elements lasting hundreds of milliseconds. During timing, only a portion of this circuit, the SMA proper and CMA, was engaged. Both timing and counting interfered with semantic processing during the resting state, evidenced by task-related decreases in the left inferior and middle frontal gyri, right superior frontal gyrus, left angular gyrus, and bilateral posterior cingulate cortex. This study suggests that counting activates a corticostriatal network associated with millisecond, rhythmic timing. In contrast, timing long durations without the benefit of linguistic strategies for subdividing counts reduces activity in this circuitry.

Adult↗

PubMed2004

Frontal-striatal circuitry activated by human peak-interval timing in the supra-seconds range.

Functional magnetic resonance imaging (fMRI) was used to measure the location and intensity of brain activations when participants time an 11-s signal duration. The experiment evaluated six healthy adult male participants who performed the peak-interval timing procedure in variants of stimulus modality (auditory or visual) and condition (foreground or background: i.e., whether the presence or absence of the stimulus is the signal to be timed). The complete experimental design called for each signal variant to be used across four behavioral tasks presented in the following order: control, timing+motor, timing, and motor. In the control task, participants passively experienced the stimuli. The timing+motor and timing tasks were preceded by five fixed-time training trials in which participants learned the 11-s signal they would subsequently reproduce. In the timing+motor task, participants made two motor responses centered around their subjective estimate of the criterion time. For the timing task, participants were instructed to time internally without making a motor response. The motor task had participants make two cued responses that were not determined by the participant's sense of the passage of time. Neuroimaging data from the timing+motor and timing tasks showed activation of the frontal cortex, striatum and thalamus--none of which was apparent in the control or motor tasks. These results, combined with other peak-interval procedure data from drug and lesion studies in animals as well as behavioral results in human patient populations with striatal damage, support the involvement of frontal-striatal circuitry in human interval timing.

Acoustic Stimulation↗

PubMed2004

"One-thousand one... one-thousand two...": chronometric counting violates the scalar property in interval timing.

Weber's law applied to interval timing is called the scalar property. A hallmark of timing in the seconds-to-minutes range, the scalar property is characterized by proportionality between the standard deviation of a response distribution and the duration being timed. In this temporal reproduction study, we assessed whether the scalar property was upheld when participants chronometrically counted three visually presented durations (8, 16, and 24 sec) as compared with explicitly timing durations without counting. Accuracy for timing and accuracy for counting were similar. However, whereas timing variability showed the scalar property, counting variability did not. Counting variability across intervals was accurately modeled by summing a random variable representing an individual count. A second experiment replicated the first and demonstrated that task differences were not due to presentation order or practice effects. The distinct psychophysical properties of counting and timing behaviors argue for greater attention to participant strategies in timing studies.

Adult↗

PubMedDate not supplied

fMRI biomarker of early neuronal dysfunction in presymptomatic Huntington's Disease.

BACKGROUND AND PURPOSE: Functional MR imaging (fMRI) has been used to probe basal ganglia function in people with presymptomatic Huntington's disease (pre-HD). A previous fMRI study in healthy individuals demonstrated activation of the basal ganglia during a time-discrimination task. The current study was designed to examine the relative sensitivity of fMRI compared with that of behavioral testing and morphometric measurements in detecting early neurodegenerative changes related to Huntington's disease (HD). METHODS: Pre-HD participants were assigned to two groups based on estimated years to diagnosis of manifest disease: close <12 years and far >or=12 years. Age at disease onset was estimated using a regression equation based on the number of trinucleotide CAG repeats. The time-discrimination task required participants to determine whether a specified interval was shorter or longer than a standard interval of 1200 milliseconds. RESULTS: Participants in the close group performed more poorly on the time-task discrimination than did control subjects; however, no differences were observed between far participants and control subjects. Similarly, close participants had reduced bilateral caudate volume relative to that of control subjects, whereas far participants did not. On functional imaging, close participants had significantly less activation in subcortical regions (caudate, thalamus) than control subjects; far participants had an intermediate degree of activation. In contrast, far participants had hyperactivation in medial hemispheric structures (anterior cingulate, pre-supplementary motor area) relative to close and control subjects. CONCLUSION: Hyperactivation of medial prefrontal regions compensated for reduced subcortical participation during time discrimination in pre-HD. This pattern of brain activation may represent an early neurobiologic marker of neuronal dysfunction.

Adult↗