The hippocampus is involved in spatial navigation and contextual memory. Hippocampal principal cells fire when a rat is in a specific place in its environment and this place cell activity can be prospectively modulated by the rat’s imminent trajectory. Here we examined whether there is a link between prospective coding and navigational decision processing. We recorded place cells in rats performing a task involving a sudden decisional switch and assessed the latency of the prospective activity onset. Rats learned to alternate (ALT) in a continuous T-maze task. Every 5 to 7 trials, a visual cue (VC) was presented as the rat crossed a photodetector at the middle of the central arm. This instructed the rat to repeat a visit to the previous arm rather than to continue alternating. Prospective activity was assessed with a bootstrap method yielding fine grained spatial resolution of differences in spike rate functions between leftward and rightward trajectories (controlling for differences in lateral position along the leftward vs rightward trajectories). This method allowed us to precisely determine where place cell responses started to change after presentation of the VC relative to ALT trials. We recorded 816 cells in 4 rats in 26 sessions. Of these, 19 neurons had prospective activity in the central arm. In 15 out of 19 cells the onset of significant prospective activity occurred further down the arm in cued trials than in alternation trials. Consistent with our hypothesis that prospective activity was triggered after a fixed time T following the cue presentation, this difference was greater for cells with place fields closer to the photodetector. A linear regression (t-test for significant slope p=0.0128) of the onset times of activity in ALT trials plotted as a function of the time difference between the activity onsets of VC and ALT trials yielded a value of T ~ 450ms. This relatively long delay for prospective activity to arise (compared, e.g., to 150 ms after cue presentation for orienting decision signals in the superior colliculus; Felsen & Mainen, 2008, Neuron, 60:137) suggests that there is substantial pre-processing before this information reaches the hippocampus, perhaps in pathways involving cortico-striatal loops. Thus the navigational behavioral choice signal is likely elaborated elsewhere, then transmitted to the hippocampus to inform prospective activity. The hippocampus would then engage this for contextual processing of memories in time and space. Recording in other areas with this type of paradigm should permit detection of the earliest appearances of navigational choice related activity.
Dynamics of decision-related activity in prospective hippocampal place cells
VIGGIANO, Alessandro;
2011
Abstract
The hippocampus is involved in spatial navigation and contextual memory. Hippocampal principal cells fire when a rat is in a specific place in its environment and this place cell activity can be prospectively modulated by the rat’s imminent trajectory. Here we examined whether there is a link between prospective coding and navigational decision processing. We recorded place cells in rats performing a task involving a sudden decisional switch and assessed the latency of the prospective activity onset. Rats learned to alternate (ALT) in a continuous T-maze task. Every 5 to 7 trials, a visual cue (VC) was presented as the rat crossed a photodetector at the middle of the central arm. This instructed the rat to repeat a visit to the previous arm rather than to continue alternating. Prospective activity was assessed with a bootstrap method yielding fine grained spatial resolution of differences in spike rate functions between leftward and rightward trajectories (controlling for differences in lateral position along the leftward vs rightward trajectories). This method allowed us to precisely determine where place cell responses started to change after presentation of the VC relative to ALT trials. We recorded 816 cells in 4 rats in 26 sessions. Of these, 19 neurons had prospective activity in the central arm. In 15 out of 19 cells the onset of significant prospective activity occurred further down the arm in cued trials than in alternation trials. Consistent with our hypothesis that prospective activity was triggered after a fixed time T following the cue presentation, this difference was greater for cells with place fields closer to the photodetector. A linear regression (t-test for significant slope p=0.0128) of the onset times of activity in ALT trials plotted as a function of the time difference between the activity onsets of VC and ALT trials yielded a value of T ~ 450ms. This relatively long delay for prospective activity to arise (compared, e.g., to 150 ms after cue presentation for orienting decision signals in the superior colliculus; Felsen & Mainen, 2008, Neuron, 60:137) suggests that there is substantial pre-processing before this information reaches the hippocampus, perhaps in pathways involving cortico-striatal loops. Thus the navigational behavioral choice signal is likely elaborated elsewhere, then transmitted to the hippocampus to inform prospective activity. The hippocampus would then engage this for contextual processing of memories in time and space. Recording in other areas with this type of paradigm should permit detection of the earliest appearances of navigational choice related activity.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
