Neural correlates of vibrotactile working memory in the human brain

Recent neurophysiological studies in macaques identified a network of brain regions related to vibrotactile working memory (WM), including somatosensory, motor, premotor, and prefrontal cortex. In these studies, monkeys decided which of two vibrotactile stimuli that were sequentially applied to their fingertips and separated by a short delay had the higher vibration frequency. Using the same task, the objective of the present study was to identify the neural correlates related to the different task periods (encoding, maintenance, and decision making) of vibrotactile WM in the human brain. For this purpose, we used event-related functional magnetic resonance imaging and contrasted WM trials with a control condition of vibrotactile stimulation that did not require maintenance and decision making. We found that vibrotactile WM has a similar but not identical neural organization in humans and monkeys. Consistent with neurophysiological data in monkeys and behavioral studies in humans, the primary somatosensory and the ventral premotor cortex exhibited increased activity during encoding. Maintenance of a vibrotactile memory trace evoked activity in the premotor and ventrolateral prefrontal cortex. Decision making caused activation in the somatosensory, premotor, and lateral prefrontal cortex. However, human vibrotactile WM recruited additional areas. Decision making activated a broader network than that studied thus far in monkeys. Maintenance and decision making additionally activated the inferior parietal lobe. Although the different task components evoked activity in distinctive neural networks, there was considerable overlap of activity, especially regarding maintenance and decision making, indicating that similar neural mechanisms are required for the subprocesses related to these task components.