Pattern association through a hippocampal loop.

<p>Panel <b>a</b>) and <b>b</b>) show the recall of two previously learned associations. Both recalls were initiated by an external cue at around 100 ms, which evoked a sparse temporal pattern in the hippocampal layers, which in turn drove the target pattern in the cortex. <b>c</b>) Average number of neurons for all four patterns during learning and recall. Grey bars indicate when patterns have been externally stimulated. <b>d</b>) Mean weight for connections between hippocampal neurons that spike in response to pattern A and C (H(A) and H(C), respectively) to target patterns B. Grey bars as in c). During the first learning phase, the connection weight increase and thereby contribute to the association of pattern A with B. Although in the second learning phase the same hippocampal neurons are also activated by pattern C, their connections to neurons of pattern B remain stable indicating that the spatio-temporal sequence of hippcampal neurons is important for storing unique associations.