When an animal makes a decision, sensory information must be transformed into an action — but this transformation is not instantaneous. Often, the brain has to hold information in short-term memory before acting on it. A central question is therefore how sensory signals travel through the cortex, where they are maintained during a delay, and whether this routing depends only on the sensory modality or also on the behavioral strategy used by the animal.
In this study, together with Fritjof Helmchen and other colleagues at University of Zurich, we used cortex-wide calcium imaging to record activity across large portions of the mouse neocortex while animals performed delayed discrimination tasks. Mice were trained either to discriminate auditory cues or to discriminate whisker-based tactile cues, and then to respond after a short delay. This design allowed the authors to compare how different sensory modalities engage cortical networks during perception, memory, and action.
The study shows that auditory and tactile stimuli initially recruit distinct sensory pathways and separate subdivisions of posterior parietal cortex. These posterior parietal subdivisions were not merely passive relays: they were causally required for performance in their respective tasks. This supports the idea that modality-specific parietal regions help route sensory information toward higher association areas.
A particularly important result concerns the delay period, when the stimulus is no longer present but must still be maintained to guide behavior. During this period, cortical activity was not determined simply by whether the original stimulus was auditory or tactile. Instead, the location of delay activity depended strongly on behavioral strategy. In active trials, delay activity converged toward frontomedial cortical regions; in passive trials, it shifted toward more posterolateral regions. In other words, short-term memory was not stored in a fixed cortical “box”: it was routed differently depending on what the animal was doing.
A useful way to summarize the finding is: the cortex does not simply pass sensory information along a fixed pipeline. It routes information dynamically, combining what the stimulus is with how the animal intends to use it.
This work highlights the importance of studying brain-wide activity during behavior. By combining wide-field calcium imaging, delayed discrimination tasks, and causal perturbations of posterior parietal cortex, the study shows how sensory modality and behavioral context jointly shape cortical signal flow. It provides a mechanistic view of short-term memory as an active, state-dependent routing process across distributed neocortical networks.
To know more:
- Gallero-Salas, Y., Han, S., Sych, Y., Voigt, F. F., Laurenczy, B., Gilad, A., & Helmchen, F. (2021). Sensory and Behavioral Components of Neocortical Signal Flow in Discrimination Tasks with Short-Term Memory. Neuron, 109, 135–148.e6. https://doi.org/10.1016/j.neuron.2020.10.017.