Ruiting Xiao

Neuroanatomical discrimination between manipulating and maintaining processes involved in verbal working memory; a functional MRI study

We used functional magnetic resonance imaging (fMRI) to investigate neural correlates of processes concerning store and manipulation in verbal working memory. We prepared a revised lag 1 digit span, digit span and a simple number detection task. Specific activities in association with manipulating process were identified in the right middle (BA 9/46) and left precentral gyrus (BA 6). Activated areas specific to maintaining process were detected in the right middle (right BA 11/10) and medial (BA 6) frontal gyri, the right inferior parietal lobule (BA 40), and the left middle (BA 9) and inferior frontal gyri (BA 44). The process-nonspecific activated areas common to two processes were identified in the right inferior frontal gyrus (BA 47) and the left superior parietal lobule (BA 7). Using the signal percent change of each subject, we calculated the correlation coefficients among each activated area. The results of this analysis showed that two processes of verbal working memory were clearly discriminated. The two essential processes of manipulation and maintenance in working memory seem to activate process-specific and overlapping (process-nonspecific) areas, but the patterns of combination were definitely different.

Medial temporal lobe activation during context-dependent relational processes in episodic retrieval: An fMRI study

Previous studies have reported that the medial temporal lobe (MTL) structures contribute to the processing of relations among multiple stimuli in episodic encoding. There have been few studies, however, on the episodic retrieval requiring processing of relations among multiple components that was involved in our events. We used functional magnetic resonance imaging (fMRI) to investigate neural activities during the retrieval of relations within an organized episode and the recognition of an episodic component. Healthy, normal participants memorized 50 four‐scene comic strips before fMRI scanning. In the retrieval phase with fMRI scanning, participants were engaged in three tasks: a visual identification (VI) task, a story recall (SR) task, and a picture recognition (PRe) task. In the VI task, participants were asked to judge whether they could identify at least one female character in the two scenes presented vertically. In the SR task, participants were shown the first and last scenes from strips memorized previously and asked to judge whether or not the two scenes were from the same strip. In the PRe task, participants were shown two scenes and asked to judge whether they both belonged to the memorized scenes. The two contrasts of SR with VI and PRe with VI demonstrated some commonly activated areas, such as the bilateral middle frontal gyrus and cerebellum. More importantly, the SR task differentially activated the bilateral parahippocampal gyrus, whereas the PRe task differentially activated right prefrontal areas, including the inferior frontal and precentral gyri. The results suggest that the activity of the MTL structures may be strongly associated with episodic memory retrieval requiring context‐dependent relational processing. Hum. Brain Mapping 17:203–213, 2002.

Different Distribution of the Activated Areas in the Dorsal Premotor Cortex during Visual and Auditory Reaction-Time Tasks

Sensorimotor association is an essential aspect of behavior. The dorsal part of the premotor cortex (PMd) is known to have an important role in sensorimotor association. Although it is suggested that the partially segregated groups of neurons are involved in sensorimotor association in different sensory modalities, it is not yet clear whether these groups occupy the PMd to the same or different extent. Therefore, we performed a functional magnetic resonance imaging study to compare activated regions in the PMd during simple reaction-time tasks with visual and auditory cues. Eight normal volunteers performed two simple reaction time tasks with a conventional on-off design; one is with a visual cue and the other is with an auditory cue. In both tasks, two regions in the left primary motor area (M1) (4a and 4p) and the bilateral PMd were activated. The two activated regions in the left M1 occupied the same areas in both the visual and the auditory tasks. However, in the PMd, the activated regions were situate medially during the visual task and laterally during the auditory task, along the precentral sulci. There was no overlap of significantly activated regions between two tasks, and areas specifically activated during the visual task were observed in the middle of the precentral sulci, bilaterally. The results suggest that the distribution of PMd subregions involved in sensorimotor association differ when the sensory cues are in different modalities.

Brain activation during picture-word association encoding — An fMRI study

To investigate the functional role of hippocampus in association memory processes, we measured human brain activation during encoding individual pictures and picture-word pairs to memory by a 3T-fMR1 system. In the individual picture encoding task, subjects were presented with unfamiliar national ensigns individually and were asked to remember them. In the picture-word association encoding task, subjects were presented with national ensigns and national names in pairs and were asked to remember their associations. Before this task, the subjects were presented with these pictures and words separately, but they did not know relationships between the national ensigns and names. Significant activation of right hippocampal formation and bilateral parahippocampal gyrus were observed in both the individual and associative encoding tasks, but the activation appeared slight stronger in the latter case than in the former case. It indicates that hippocampus might participate in memory process of picture-word associations as well as in memory process of individual pictures, but with different degrees of contributions.

An FMRI study of the dorsolateral prefrontal cortex activation during non-spatial verbal working memory tasks

To investigate the functional role of hippocampus in association memory processes, we measured human brain activation during encoding individual pictures and picture-word pairs to memory by a 3T-fMR1 system. In the individual picture encoding task, subjects were presented with unfamiliar national ensigns individually and were asked to remember them. In the picture-word association encoding task, subjects were presented with national ensigns and national names in pairs and were asked to remember their associations. Before this task, the subjects were presented with these pictures and words separately, but they did not know relationships between the national ensigns and names. Significant activation of right hippocampal formation and bilateral parahippocampal gyrus were observed in both the individual and associative encoding tasks, but the activation appeared slight stronger in the latter case than in the former case. It indicates that hippocampus might participate in memory process of picture-word associations as well as in memory process of individual pictures, but with different degrees of contributions.

Neuroanatomical basis of manipulation of short-term verbal information; evidence from functional MRI

To investigate the functional role of hippocampus in association memory processes, we measured human brain activation during encoding individual pictures and picture-word pairs to memory by a 3T-fMR1 system. In the individual picture encoding task, subjects were presented with unfamiliar national ensigns individually and were asked to remember them. In the picture-word association encoding task, subjects were presented with national ensigns and national names in pairs and were asked to remember their associations. Before this task, the subjects were presented with these pictures and words separately, but they did not know relationships between the national ensigns and names. Significant activation of right hippocampal formation and bilateral parahippocampal gyrus were observed in both the individual and associative encoding tasks, but the activation appeared slight stronger in the latter case than in the former case. It indicates that hippocampus might participate in memory process of picture-word associations as well as in memory process of individual pictures, but with different degrees of contributions.