Mechanisms of sustained rehearsal in tactile short-term memory

• Applicant: Dr. Tobias Katus
• Subject Area: General, Cognitive and Mathematical Psychology ; Human Cognitive and Systems Neuroscience
• Term: from 2013 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 237675329

• Final Report Year: 2016

Final Report Abstract

This research project used electroencephalography (EEG) to shed light on storage- and attention-related processes involved in tactile working memory (WM). Contrary to the widespread view that tactile information are stored in multisensory / amodal cortical regions, our results suggest that tactile information are stored in a dedicated memory system that encompasses somatosensory cortex. We found load-dependent modulations of somatosensory neural activity during the retention of tactile signals, and furthermore observed that the spatial layout of tactile WM representations mirrors the somatotopic organization of somatosensory cortex. These results support a sensory recruitment account, which states that information is stored in the same perceptual brain regions that have encoded this information into WM. We discovered a novel EEG marker for the sustained attentional maintenance of somatotopic information in WM (tactile contralateral delay activity, tCDA). The tCDA is sensitive to tactile WM load and has a modality-specific topography over somatosensory cortex, and thus, appears to be the tactile counterpart of the well-known visual CDA component. Our second line of investigations suggests that the tCDA does not directly reflect the storage, but the attentional activation of tactile information, and furthermore, demonstrates that this activation process is mediated by an attentional mechanism that is shared with perception. These theoretical and methodological advances led to a further, currently ongoing, line of investigation. In multisensory WM tasks, we used the tactile and visual CDA components to track the attentional activation states of tactile and visual WM representations concurrently. Preliminary results indicate that distinct types of attentional processes mediate the selection of tactile and visual WM content, pointing to the conclusion that WM relies on distributed mechanisms - not only for the storage - but also for the attentional activation of WM content. Overall, the project has led to exciting new insights into the neural underpinnings of tactile WM. It revealed a novel marker for sustained tactile attention, and it demonstrated that it is possible to track tactile and visual attention during multimodal WM tasks simultaneously. The project's original questions were fully answered by our experiments.

Publications

• (2015) Electrophysiological evidence for a sensory recruitment model of somatosensory working memory. Cereb Cortex, 25, 4697–4703
  Katus T, Grubert A, Eimer M
  
• (2015) Sustained maintenance of somatotopic information in brain regions recruited by tactile working memory. J Neurosci, 35, 1390-95
  Katus T, Müller MM, Eimer M
  
• (2015) The role of spatial attention in tactile short-term memory. In P Jolicoeur, C Lefebvre, J Martinez-Trujillo (Eds.), Mechanisms of Sensory Working Memory: Attention and Performance XXV. Oxford, UK: Elsevier
  Katus T, Andersen SK
  
• (2015). Inter-modal attention shifts trigger the selective activation of task-relevant tactile or visual working memory representations. 15th meeting of the Vision Sciences Society, St. Pete Beach, FL
  Katus T, Grubert A, Eimer M
  
• (2015). Lateralized delay period activity marks the focus of spatial attention in working memory: evidence from somatosensory event-related brain potentials. J Neurosci, 35, 6689-95
  Katus T, Eimer M
  
• (2016). Working memory delay period activity marks a domainunspecific attention mechanism. NeuroImage, 128, 149-57
  Katus T, Müller MM