Fig. 6.
Variations in correlated activity with movement direction. A, A cell pair showing strong trial-by-trial covariation in firing for movements in the 135° direction (left) but much weaker covariation for movements in the 315° direction. The normalized firing rates of one cell (open squares and dashed line) are plotted together with those of another cell (solid circles andsolid line) over all trials in the recording session. Whereas the normalized firing rates are significantly correlated for 135° movements (rij = 0.85;p < 0.001), they are not significantly correlated for 315° movements (rij = 0.05;p < 0.79). B, Variations in the firing rates of two cells (top) and in their correlation coefficient (bottom) over eight movement directions. The two cells fire maximally in the 135° direction, whereas their peak correlation occurs in the 45 and 270° directions.