Figure 8.

Comparison of the velocity correlation for LDTg, PPTg, and VTA neurons. A) (Top) The mean (+) SE velocity correlation coefficient is shown for pre-reward, reward encounter, and velocity (only) LDTg neurons. Velocity correlations for the entire recording session were compared between Blocks 1 and 2. While there were no effects of Block, reward encounter cells were more strongly correlated with velocity than pre-reward or velocity (only) cells. The scatterplot inset compares individual cell correlations for Block 1 vs Block 1. Pre-reward cells (shown by the red dots) were either strongly positively or strongly negatively correlated with velocity. In contrast, reward encounter cells (blue dots) were only negatively correlated with velocity. (Bottom) The velocity correlation of LDTg neurons as rats approached reward locations on the maze (outbound), or as rats began to move inward on the maze arms towards the central platform (inbound) after making a 180 degree turn at the maze arm ends. Pre-reward cell firing was more strongly correlated with velocity when rats moved outbound than inbound, an effect not observed for reward encounter or velocity (only) cells. [Note: a single dot in the scattergram inset may correspond to more than one cell with the same r-value] The velocity correlation value is much higher for reward encounter cells in the top figure because that summary included velocities during behaviors that were not included in the bottom figure (e.g. turns at the arm ends and crossing the central platform). B) Pedunculopontine (PPTg) neural activity that was reported in a study by Norton et al. (2011) was reanalyzed here so that direct comparisons could be made to the LDTg responses. Top In contrast to LDTg responses, PPTg reward encounter cells (bar graphs) showed weaker correlations relative to pre-reward and velocity (only) cells. The scatterplot shows that while pre-reward PPTg cells (red dots) showed only positive correlations that were not sensitive to reward manipulations that occurred in Block 2 trials, the activity of PPTg reward encounter cells (blue dots) were more weakly positive or negatively correlated with velocity. Bottom Unlike LDTg, PPTg neurons did not show different velocity correlations during outbound and inbound movements trajectories. The scatterplot, however, illustrates that while some of the PPTg neurons showed stronger velocity correlations in the outbound direction, many did not. C) Ventral tegmental (VTA) neural activity that was acquired by Puryear et al. (2010) was reanalyzed here so that direct comparisons could be made to the LDTg and PPTg responses. Top Similar to PPTg, there was no change across Blocks of trials in terms of the velocity correlation coefficient for any type of cell response. However velocity (only) cells showed stronger correlations with velocity than especially the reward encounter cells. In the scatterplot inset it can be seen that while reward encounter cells (blue dots) showed a range of positive and negative correlations with velocity, pre-reward cells (red dots) showed predominantly positive correlations. Bottom Also similar to PPTg neural responses, there was no significant difference in velocity correlation as rats moved in the outbound and inbound directions. D) A comparison of the behaviors of rats from this (LDTg) and our earlier studies of PPTg and VTA neural activity is shown in terms of the velocity of the rats’ movements toward (left) and away from (right) the goal location. It can be seen that the pattern if changes in velocity are nearly identical. Thus the differential responses of these groups of cells during outbound and inbound trajectories cannot be accounted for by different patterns of behaviors across the studies. E) Mean velocity for the LDTg, PPTg, and VTA populations of recorded neurons during outbound (left) and inbound (right) trajectories. It can be seen that the average firing rates did not differ across groups, or as a function of direction of movement.