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Purpose: Working memory (WM) represents the brain’s ability to maintain information in a readily available state for short periods of time. This study examines the resting-state cortical activity patterns that are most associated with performance on a difficult working-memory task. Methods: Magnetoencephalographic (MEG) band-passed (delta/theta (1–7 Hz), alpha (8–13 Hz), beta (14–30 Hz)) and sensor based regional power was collected in a population of adult men (18–28 yrs, n = 24) in both an eyes-closed and eyes-open resting state. The normalized power within each resting state condition as well as the normalized change in power between eyes closed and open (zECO) were correlated with performance on a WM task. The regional and band-limited measures that were most associated with performance were then combined using singular value decomposition (SVD) to determine the degree to which zECO power was associated with performance on the three-back verbal WM task. Results: Changes in power from eyes closed to open revealed a significant decrease in power in all band-widths that was most pronounced in the posterior brain regions (delta/theta band). zECO right posterior frontal and parietal cortex delta/theta power were found to be inversely correlated with three-back working memory performance. The SVD evaluation of the most correlated zECO metrics then provided a singular measure that was highly correlated with three-back performance (r = −0.73, p<0.0001). Conclusion: Our results indicate that there is an association between WM performance and changes in resting-state power (right posterior frontal and parietal delta/theta power). Moreover, an SVD of the most associated zECO measures produces a composite resting-state metric of regional neural oscillatory power that has an improved association with WM performance. To our knowledge, this is the first investigation that has found that changes in resting state electromagnetic neural patterns are highly associated with verbal working memory performance. [ABSTRACT FROM AUTHOR]

Despite numerous studies in which hippocampal abnormalities were found, schizophrenia patients' hippocampal neural activity has not been systematically evaluated on a specific hippocampal-dependent task. The transverse-patterning task (TP) is sensitive to the relational mnemonic capabilities of the hippocampus. Ten schizophrenia patients and 10 controls performed TP and control tasks that are not hippocampal dependent. As predicted, patients displayed a behavioral impairment in TP and not in control tasks. Magnetoencephalography showed controls activating right hippocampus during TP performance. Patients showed more bilateral or left hippocampal activation during TP, and greater left lateralization was associated with better performance on TP. Patients' abnormal hippocampal lateralization may play a role in the hippocampal-dependent behavioral deficit. [ABSTRACT FROM AUTHOR]

Abstract: Auditory response profiles for a group of ten healthy young and ten healthy elderly subjects, evoked by implicit memory and delayed verbal recognition tasks, were evaluated to determine if effects of stimulus repetition could be identified in the superior temporal gyrus (STG) and prefrontal cortical regions. We hypothesized that effects of stimulus repetition should occur both early in time and at early levels of the nervous system (STG) followed by later effects in prefrontal regions. Magnetoencephalographic (MEG) responses were recorded using a whole-head MEG system and automated, multi-start analysis methods were applied to the data in order to characterize the temporal response profiles from distributed but focal, cortical regions engaged in memory-related tasks. The findings revealed a main effect of age for early activity (∼50 ms) in STG which appeared to be nonspecific for Old/New words and an Age × Task interaction for late activity (∼100–800 ms) in STG which was specific to Old/New words. Although the behavioral performance measures did not reveal traditional effects of response priming, the MEG measures did reveal a reduction in amplitude with stimulus repetition in young subjects. The elderly did not reveal a reduction in amplitude concomitant with stimulus repetition for either the global attributes of words or for specific Old/New words. Long duration effects of stimulus repetition noted in the present study raise the possibility that results from sensory gating, mismatch negativity and P300 paradigms may represent a continuum of stimulus repetition effects. Two of these paradigms evoke greater enhancement to novel or infrequent stimuli, or rather, greater reduction of amplitude with repetition. [Copyright &y& Elsevier]

Our perception of time depends on multiple psychological processes that allow us to anticipate events. In this study, we used event-related functional magnetic resonance imaging (fMRI) to differentiate neural systems involved in formulating representations of time from processes associated with making decisions about their duration. A time perception task consisting of two randomly presented standard intervals was used to ensure that intervals were encoded on each trial and to enhance memory requirements. During the encoding phase of a trial, activation was observed in the right caudate nucleus, right inferior parietal cortex and left cerebellum. Activation in these regions correlated with timing sensitivity (coefficient of variation). In contrast, encoding-related activity in the right parahippocampus and hippocampus correlated with the bisection point and right precuneus activation was associated with a measure of memory distortion. Decision processes were studied by examining brain activation during the decision phase of a trial that was associated with the difficulty of interval discriminations. Activation in the right parahippocampus was greater for easier than harder discriminations. In contrast, activation was greater for harder than easier discriminations in systems involved in working memory (left middle-frontal and parietal cortex) and auditory rehearsal (left inferior-frontal and superior-temporal cortex). Activity in the auditory rehearsal network correlated with memory distortion. Our results support the independence of systems that mediate interval encoding and decision processes. The results also suggest that distortions in memory for time may be due to strategic processing in cortical systems involved in either encoding or rehearsal. [Copyright &y& Elsevier]