Models of spatial and temporal dimensions of memory

Abstract

Episodic memory involves coding of the spatial location and time of individual events. Coding of space and time is also relevant to working memory, spatial navigation, and the disambiguation of overlapping memory representations. Neurophysiological data demonstrate that neuronal activity codes the current, past and future location of an animal as well as temporal intervals within a task. Models have addressed how neural coding of space and time for memory function could arise, with both dimensions coded by the same neurons. Neural coding could depend upon network oscillatory and attractor dynamics as well as modulation of neuronal intrinsic properties. These models are relevant to the coding of space and time involving structures including the hippocampus, entorhinal cortex, retrosplenial cortex, striatum and parahippocampal gyrus, which have been implicated in both animal and human studies.

Figure 1

A. Computation of the location of an animal in a square environment with barriers can be determined from the angle and distance to visual features [47]. Movement of barriers has been shown to shift neurophysiological codes for location [15,18]. B. Figure showing the egocentric view of visual features at location in A. C–D. Same as A–B for a different location.

Figure 2

A. Model for goal-directed behavior based on linear forward trajectory planning [68]. Circles represent the location where previous place cell firing took place. Triangle indicates animal location. Light gray lines indicate sequential sampling of forward trajectories through the environment. Darker line ending in circle indicates the trajectory that overlaps with the previously visited place cell firing field that was associated with a goal location, allowing selection of this trajectory. B. Different trajectories obtained by sampling at multiple spatial scales, allowing initial selection of trajectories to the large place cell firing field, followed by selection of trajectories to smaller place cell firing fields.

Figure 3

Coding of space and time by the oscillatory interference model [29,60]. A. The model simulates grid cell firing as a simulated rat runs on a foraging trajectory (gray lines). Black dots show the location of the simulated rat each time the grid cell model generates a spike. B. The same model addresses activity during spatial alternation on a T-maze (top) with a period of running on a running wheel during the delay period between choices (lines on bottom). C. The same model shows location dependent firing on the T-maze (dark segments in top plot) as well as consistent firing at specific intervals of time or distance during running on the running wheel (dark segments on bottom lines).