Xiangchuan Chen

Age-dependent brain activation during forward and backward digit recall revealed by fMRI

In this study, brain activation associated with forward and backward digit recall was examined in healthy old and young adults using functional MRI. A number of areas were activated during the recall. In young adults, greater activation was found in the left prefrontal cortex (BA9) and the left occipital visual cortex during backward digit recall than forward digit recall. In contrast, the activation in the right inferior frontal gyrus (BA 44/45) was more extensive in forward digit recall than in backward digit recall. In older adults, backward recall generated stronger activation than forward recall in most areas, including the frontal, the parietal, the occipital, and the temporal cortices. In the backward recall condition, the right inferior frontal gyrus (BA44/45) showed more activation in the old group than in the young group. These results suggest that different neural mechanisms may be involved in forward and backward digit recall and brain functions associated with these two types of recall are differentially affected by aging.

A functional MRI study of high-level cognition

GO is a board game thought to be different from chess in many aspects, most significantly in that GO emphasizes global strategy more than local battle, a property very difficult for computer programs to emulate. To investigate the neural basis of GO, functional magnetic resonance imaging (fMRI) was used to measure brain activities of subjects engaged in playing GO. Enhanced activations were observed in many cortical areas, such as dorsal prefrontal, parietal, occipital, posterior temporal, and primary somatosensory and motor areas. Quantitative analysis indicated a modest degree of stronger activation in right parietal area than in left. This type of right hemisphere lateralization differs from the modest left hemisphere lateralization observed during chess playing.  2002 Elsevier Science B.V. All rights reserved. Theme: Neural basis of behaviour

Binding of verbal and spatial information in human working memory involves large-scale neural synchronization at theta frequency

Whether neural synchronization is engaged in binding of verbal and spatial information in working memory remains unclear. The present study analyzed oscillatory power and phase synchronization of electroencephalography (EEG) recorded from subjects performing a working memory task. Subjects were required to maintain both verbal (letters) and spatial (locations) information of visual stimuli while the verbal and spatial information were either bound or separate. We found that frontal theta power, and large-scale theta phase synchronization between bilateral frontal regions and between the left frontal and right temporal-parietal regions were greater for maintaining bound relative to separate information. However, the same effects were not observed in the gamma band. These results suggest that working memory binding involves large-scale neural synchronization at the theta band.

The effect of visuospatial attentional load on the processing of irrelevant acoustic distractors

This work investigated the role of cognitive control functions in selective attention when task-relevant and -irrelevant stimuli come from different sensory modalities. We parametrically manipulated the load of an attentive tracking task and investigated its effect on irrelevant acoustic change-related processing. While subjects were performing the visual attentive tracking task, event-related potentials (ERPs) were recorded for frequent standard tones and rare deviant tones presented as auditory distractors. The deviant tones elicited two change-related ERP components: the mismatch negativity (MMN) and the P3a. The amplitude of the MMN, which indexes the early detection of irregular changes, increased with increasing attentional load, whereas the subsequent P3a component, which indicates the involuntary orienting of attention to deviants, was significant only in the lowest load condition. These findings suggest that active exclusion of the early detection process of irrelevant acoustic changes depends on available resources of cognitive control, whereas the late involuntary orienting of attention to deviants can be passively suppressed by high demand on central attentional resources. The present study thus reveals opposing visual attentional load effects at different temporal and functional stages in the rejection of deviant auditory distractors and provides a new perspective on the resolution of the long-standing early versus late attention selection debate.

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.

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.

Temporal characteristics of binocular rivalry: visual field asymmetries.

Very little is known about the mechanisms that drive the alternation between the two views during binocular rivalry. A key property of the rivalry process is the rate at which the two views alternate. Understanding the factors that affect the rate of the alternation is critical to the final understanding of the underlying process. Using a circular and a radial grating as the rivalry stimuli, we observed a significantly faster binocular rivalry when stimuli were presented in the right visual field than that in the left visual field for the right-handed observers, and a reversed asymmetry for the left-handed observers. In both groups, rivalry was faster for stimuli presented in the lower visual field than that in the upper visual field. This pattern of results suggests that (1) rivalry is likely a locally driven process and (2) the visual brain in the left hemisphere may be the faster one of the two hemispheres in right-handed people.

Masked smoking-related images modulate brain activity in smokers

The questions of whether and how indiscriminate drug‐related stimuli could influence drug‐users are important to our understanding of addictive behavior, but the answers are still inconclusive. In the present preliminary functional magnetic resonance imaging study using a backward masking paradigm, the effect of indiscriminate smoking‐related stimuli on 10 smokers and 10 nonsmokers was examined. The BOLD response showed a significant reduction (P = 0.001) in the right amygdala of smokers when they viewed but did not perceive masked smoking‐related stimuli, while no significant differences were found in the nonsmoker group. More voxels in anterior cingulate cortex were negatively correlated with the amygdala during the masked smoking‐related picture condition in smokers but not in nonsmokers, whereas more positively correlated voxels were observed during the masked neutral condition. The BOLD response in drug‐users indicates the amygdala responds to drug‐related stimuli that are below the perceptual threshold. The functional connectivity data suggest a functional interaction between the amygdala and the anterior cingulate cortex when drug users view 33ms back‐masked drug‐related stimuli. This observation suggests that the amygdala plays an important role in the indiscriminate drug‐related cue process. Hum Brain Mapp, 2009.

Attention shift in human verbal working memory: Priming contribution and dynamic brain activation

When multiple items in working memory need to be accessed and manipulated, the internal attention should switch between them and, this switching process is time consuming. However, it is not clear how much of this switching cost is due to the existence or absence of the stimulus identification priming. With a figure identification and counting task, we demonstrate a small but significant priming contribution to this attention-switching cost. Furthermore, through 64-channel event-related potential (ERP) recordings, we found two ERP correlates (at 280 ms and 388 ms) of this internal attention-switching function. Source localization analysis shows dynamic brain activation starts from the temporal-occipital region and finishes in the left prefrontal cortex. The occipital-prefrontal and cingulate-prefrontal co-activations were orderly observed. We discuss the present ERP results along with our previous fMRI findings and suggest a dominant role of the left prefrontal cortex associated with attention shifts in verbal working memory.

A NEW QUANTITATIVE METHOD IN ANALYSING THE EXPERIMENTS ON SHORT TERM SERIAL MEMORY

A new quantitative method is introduced into the analysis of the experiments on short term serial memory (STSM). In this method, three parameters are defined to quantitatively represent the performance of memory for item and time order information. These parameters are the divergence, the disorder and the similarity. This method is used in analysing the experiments on visuo-spatial STSM. The results show that the parameters may reflect some characteristics of STSM.