Spatiotemporal characteristics of hemodynamic changes in the human lateral prefrontal cortex during working memory tasks

doi:10.1016/S1053-8119(03)00412-9

NeuroImage

Volume 20, Issue 3, November 2003, Pages 1493-1504

https://doi.org/10.1016/S1053-8119(03)00412-9 Get rights and content

Abstract

The prefrontal cortex (PFC) is widely believed to subserve mental manipulation and monitoring processes ascribed to the central executive (CE) of working memory (WM). We attempted to examine and localize the CE by functional imaging of the frontal cortex during tasks designed to require the CE. Using near-infrared spectroscopy, we studied the spatiotemporal dynamics of oxygenated hemoglobin (oxy-Hb), an indicator of changes in regional cerebral blood flow, in both sides of lateral PFC during WM intensive tasks. In most participants, increases in oxy-Hb were localized within one subdivison during performance of the n-back task, whereas oxy-Hb increased more diffusely during the random number generation (RNG) task. Activation of the ventrolateral PFC (VLPFC) was prominent in the n-back task; both sustained and transient dynamics were observed. Transient dynamics means that oxy-Hb first increases but then decreases to less than 50% of the peak value or below the baseline level before the end of the task. For the RNG task sustained activity was also observed in the dorsolateral PFC (DLPFC), especially in the right hemisphere. However, details of patterns of activation varied across participants: subdivisions commonly activated during performance of the two tasks were the bilateral VLPFCs, either side of the VLPFC, and either side of the DLPFC in 4, 2, and 4 of the 12 participants, respectively. The remaining 2 of the 12 participants had no regions commonly activated by these tasks. These results suggest that although the PFC is implicated in the CE, there is no stereotyped anatomical PFC substrate for the CE.

Section snippets

Participants

Twelve right-handed paid volunteers (age range, 21–29, male 11, female 1) participated in this study. None had a history of neurological illness, head injury, or substance abuse. Prior to each study, written informed consent was obtained from all participants. All participants were given practice with the tasks.

Near-infrared spectroscopy instruments

A multichannel NIRS imaging system (OMM-2000, Shimadzu Co.) and a single-channel time-resolved spectroscopy instrument (TRS-10, Hamamatsu Photonics KK) were employed. Three wavelengths

Task performance

As is typical with simple cognitive tasks, the mean responses accuracy was high and the distribution of scores was negatively skewed. Accuracies for the 1-, 2-, and 3-back tasks were 98 ± 4.01 (mean ± SD), 93 ± 8, and 83 ± 24%, respectively, while two participants showed extremely poor task performance in the 3-back task (Table 2). Randomness was evaluated by counting bias (CA, the tendency to count in ascending or descending series in steps of 1), interval bias (IB, the tendency to produce

Spatial characteristics

It is thought that the n-back task requires manipulations and monitoring in addition to active maintenance, and it has been reported that both the VLPFC and the DLPFC are activated during performance of the verbal n-back task Braver et al., 1997, D'Esposito et al., 1998. However, the present study has demonstrated that the VLPFC mainly contributes to the n-back task. This might be explained by the fact that once participants find a strategy, they can automatically perform even the 3-back task,

Conclusion

Much theoretical and experimental work has combined to suggest specific loci and roles for working memory processes in the frontal cortex. Although our study supports some functional segregation, two different working memory tasks selectively activated different regions in the PFC, it also demonstrated that there are overlaps in brain activations across the tasks in each participant. However, our data on nonsustained activation and differences in commonly activated areas between participants

Acknowledgements

This study was partially funded by the Asian Office of Aerospace Research and Development, Tokyo, Japan.

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Regular articleSpatiotemporal characteristics of hemodynamic changes in the human lateral prefrontal cortex during working memory tasks

Abstract

Section snippets

Participants

Near-infrared spectroscopy instruments

Task performance

Spatial characteristics

Conclusion

Acknowledgements

NeuroImage

Cogn. Brain Res.

Neurosci. Biobehav. Rev.

Cogn. Brain Res.

Trends Neurosci.

Neurosci. Lett

NeuroImage

Neurosci. Lett.

Working memory

The central executivea concept and some misconceptions

J. Int. Neuropsychol. Soc.

Working memory

Determionation of language dominance using functional MRIa comparison with the Wada test

Neurology

Temporal dynamics of brain activation during a working memory task

Nature

The role of prefrontal cortex in working memoryexamining the contents of consciousness

Philos. Trans. R. Soc. London Ser. B

Cortical areas and the selection of movementa study with positron emission tomography

Exp. Brain Res.

Estimation of optical pathlength through tissue from direct time of flight measurement

Phys. Med. Biol.

Regular article
Spatiotemporal characteristics of hemodynamic changes in the human lateral prefrontal cortex during working memory tasks