Numerical magnitude modulates temporal comparison: an ERP study.

Time is believed to be a part of the generalized magnitude system just like space and quantity. Previous research suggests that time perception can be affected by magnitude in some non-temporal dimensions. Here we address two questions. First, could the influence be caused by an abstract magnitude component without perceptual variables? Second, what are the underlying mechanisms of the influence? Participants compared a pair of durations defined by two Arabic digits in a hundreds of milliseconds range. They performed more accurately when the shorter durations were defined by lower numeric value digits (small digits) and the longer durations were defined by higher value digits (large digits) than they did in the reversed condition. Event-Related Potential (ERP) results showed that the CNVs corresponding to the first duration (CNV1), to the second duration (CNV2) and the N1 were all enhanced when durations marked by small digits than that marked by large ones. Combining the electrophysiological data with the behavioral results, we suggest that digits can modulate performance of temporal comparison at the relatively early stage of perceptual processing. One possible explanation of the current results is that selective temporal attention and subsequent expectation may be involved in this modulation.

fMRI revealed neural substrate for reversible working memory dysfunction in subclinical hypothyroidism.

Cognitive impairments have been found in thyroid hormone-related diseases (e.g. hyperthyroidism and hypothyroidism) for a long time. However, whether and how subclinical hypothyroidism (SCH) causes any deficits in brain functions, and whether a hormone-replacement treatment is necessary for SCH patients, still remain controversial subjects. In the present study, functional MRI (fMRI) was used to measure brain functions by asking euthyroid subjects, hyperthyroid patients and SCH patients to perform the widely used digit n-back working memory task. After having been treated with l-thyroxine for approximately 6 months, the SCH patients were asked to do the same fMRI experiment. The hypothyroid and SCH patients scored significantly lower in the 2-back task than either the hyperthyroid patients or the euthyroid subjects (P < 0.012). The fMRI showed that a common frontoparietal network, including bilateral middle/inferior frontal gyri (M/IFG), bilateral dorsolateral prefrontal cortex (DLPFC), bilateral premotor areas (PreMA), the supplementary motor area/anterior cingulate cortex (SMA/ACC) and bilateral parietal areas (PA), was activated by the n-back task in all the subjects. Further quantitative analysis showed that the load effect of blood oxygen level-dependent (BOLD) response appeared in all the five regions of interest (ROIs) in the euthyroid and hyperthyroid subjects. In the pre-treatment SCH patients, however, the load effect of BOLD response was only found in the PA and PreMA, but not in other frontal cortex ROIs [general linear model (GLM), F < 2.6, P > 0.1]. After an approximately 6 month treatment with LT4, the SCH patients exhibited the same load effects in all five ROIs as the euthyroid subjects (GLM, F > 6, P < 0.05) along with an improvement of performance in n-back task. These results suggest that working memory (but not other memory functions) is impaired in SCH patients, mainly as far as disorders of the frontoparietal network were concerned. Both the memory performance and frontal executive functions were improved after an l-thyroxine-replacement treatment.

Backward inhibition in a task of switching attention within verbal working memory.

Three experiments were conducted to examine the backward inhibition effect in attention switching within verbal working memory. Experiment one showed significant backward inhibition effect in a "tri-count task". Experiment two suggested that the effect was not due to a perceptual inhibition on the previously presented figure. Experiment three excluded the sequential expectancy explanation for this inhibition effect. Our results suggest that attention switching between working memory items is accompanied by inhibition of the previously attended working memory item. The findings are discussed in respect to the account of the executive function.

Functional comparison of primacy, middle and recency retrieval in human auditory short-term memory: an event-related fMRI study.

Primacy and recency effects refer to the better performance or shorter response time on the first and last items than the middle ones of a memory list. In order to investigate its neural basis in auditory short-term memory, event-related fMRI was used to measure brain activities when subject was recalling the first, the last, or the middle items. Recalling the middle item was associated with more extensive activation in the left parietal and visual cortex, basal ganglia, and dorsal cerebellum. Recalling items from different serial positions also resulted in different activation time courses in the bilateral primary auditory cortex, left prefrontal cortex and left premotor cortex. These data indicate that the auditory cortex may serve as a transient storage or the auditory input buffer, which seems to play an important role in the primacy and recency effects.