Neural bases of working memory and application for imminent action

Task leader: LPPA.

Comparisons of recordings in animals performing tasks with different memory requirements will reveal neurophysiological mechanisms of coding of the fundamental linking together of brief series of events. Signals to switch intention will also be employed as probes.

Aim

The objective here is to characterize the neural processing in the Hpc-Pfc-Str system for working memory processes at short time scales.

The approach is to take three versions of a task which respectively involve

  1. no working memory requirement at all (a visually cued choice),
  2. immediate working memory (alternation),
  3. working memory at longer delays (visual cue task with delay, or delayed alternation). 

Comparison of the neural activity in these tasks will permit us to distinguish those physiological processes determinant for memory function, and also to pinpoint where in the system this originates by examining the order of activation of the respective areas. Simultaneously recorded data in different structures will be examined for correlated firing. While this will focus on activity of simultaneously recorded single units, the ensemble and local field potential data recorded during the acquisition of these tasks, and as the rats shift between these tasks will be analyzed.

Subtask 1

The objective here is to characterize the neural processing in the Hpc-Pfc-Str system for working memory processes at short time scales. The approach is to take three versions of a task which respectively involve 1) no working memory requirement at all (a visually cued choice), 2) immediate working memory (alternation), 3) working memory at longer delays (visual cue task with delay, or delayed alternation). Comparison of the neural activity in these tasks will permit us to distinguish those physiological processes determinant for memory function, and also to pinpoint where in the system this originates by examining the order of activation of the respective areas. Simultaneously recorded data in different structures will be examined for correlated firing. While this will focus on activity of simultaneously recorded single units, the ensemble and local field potential data recorded during the acquisition of these tasks, and as the rats shift between these tasks will be analyzed.

A,B) The behavioral task permitting distinction of prospective active and exact onset time. B) The rat must go to the goal without the stripe cue. C) The sequence of trials: five alternation trials, then a visual cue trial (yellow background); arrows show rewarded arm.


Subtask 2 - Characterizing coding of reward-motivated memory functions in the prefrontal

The objective of this study is to determine how neuronal activity in the medial prefrontal cortex (Pfc, comprising prelimbic and infralimbic areas) is linked to executive processing and working memory. The approach is to compare activity in versions of the same task where memory of (previously learned) rewarded locations is required or not.

Subtask 3 - Is there a hippocampal/prefrontal interaction for reward-motivated memory functions?

The Pfc receives a direct projection from the hippocampus (Jay et al., 1995) suggesting that there is some interaction between these two structures. In particular, the hippocampal place cell system may provide some spatial information to the neurons of these areas. Since the activity of hippocampal neurons have been shown to be modulated by episodic aspects of the task, the prefrontal cortex and the hippocampus may also cooperate for encoding those aspects. To investigate these interactions, we will perform simultaneous unit recordings in the hippocampus and the Pfc in this subtask.