Figure 10.

A, Left, As a result of egestive repetition priming, there is a persistent increase in the excitability of B20 and use-dependent potentiation of B20-B8 synaptic transmission. Additionally, there is a decrease in the excitability of B40. Right, CBI-2 makes a fast excitatory synaptic connection with B20. Consequently, when there is a task switch, B20 fires at an elevated frequency, and the protraction phase firing frequency of B8 is elevated. Additionally, CBI-2 less effectively activates B40, and there is relatively little excitatory drive to B8 during the retraction phase of the motor program. Overall activity is egestive (i.e., negative biasing is observed). B, Left, As a result of positive biasing, the excitability of B65 and B40 is increased. Right, However, B65 is inhibited by CBI-2. Consequently, it does not fire when activity is subsequently triggered by CBI-2 and does not excite B8 during protraction. Additionally, positive biasing does not decrease the B40 excitability. Consequently, it is effectively driven by CBI-2 and provides excitatory input to B8 during retraction. Overall activity is ingestive. A, B, Green represents an increase in excitability or a potentiation of synaptic transmission. Red represents a decrease in excitability. Filled circles represent inhibitory synaptic connections. Filled triangles represent excitatory connections. A triangle with an “s” represents a slow synaptic connection.