Evidence for abstract codes in parietal cortex guiding prospective working memory

Abstract

The recent past helps us predict and prepare for the near future. Such preparation relies on working memory (WM) which actively maintains and manipulates information providing a temporal bridge. Numerous studies have shown that recently presented visual stimuli can be decoded from fMRI signals in visual cortex (VC) and the intra-parietal sulcus (IPS) suggesting that these areas sustain the recent past. Yet, in many cases, concrete, sensory signals of past information must be transformed into the abstract codes to guide future cognition. However, this process remains poorly understood. Here, human participants used WM to maintain a separate spatial location in each hemifield wherein locations were embedded in a learned spatial sequence. On each trial, participants made a sequence-match decision to a probe and then updated their WM with the probe. The same abstract sequence guided judgments in each hemifield, allowing the separate detection of concrete spatial locations (hemifield-specific) and abstract sequence positions (hemifield-general), and also tracking of representations of the past (last location/position) and future (next location/position). Consistent with previous reports, concrete past locations held in WM could be decoded from VC and IPS. Moreover, in anticipation of the probe, representations shifted from past to future locations in both areas. Critically, we observed abstract coding of future sequence positions in the IPS whose magnitude related to speeded performance. These data suggest that the IPS sustains abstract codes to facilitate future preparation and reveal a transformation of the sensory past into abstract codes guiding future behavior. Significant StatementTo act efficiently, we must use the recent past to prepare for what comes next. For this purpose, working memory (WM) is critical. Although substantial research has shown that WM retains recently presented sensory information, preparation for the future involves abstraction wherein shared meaning is aggregated while superfluous sensory details are discarded. The mechanisms underlying this process remain unclear. Analyzing functional MRI signals in the intraparietal sulcus (IPS), we found that distinct sensory states with shared predictive meaning were initially maintained in a sensory-like fashion, but over time, became aggregated indicative of abstraction. Abstraction was associated with behavioral efficiency highlighting its role in preparation. These findings reveal neural mechanisms supporting the transformation from past to future in WM.