6.4 Biological substrates
The first investigations of the biological substrates of the clock and memory stages of the pacemaker– accumulator IP model used pharmacological manipulations, and provided considerable support for a dissociation between the clock stage, which is affected by dopaminergic manipulations, and the memory stage, which is affected by cholinergic manipulations (FIG. 3a). For example, dopaminergic drugs selectively affect the subjective speed of an internal clock in both animals and humans(FIG. 3c), whereas cholinergic drugs alter memory storage (FIG. 3f). More specifically, dopaminergic antagonists produce a deceleration of the subjective clock speed (FIG. 3d) in proportion to their affinity for the dopamine D2 receptor (FIG. 3e), whereas cholinergic activity in the frontal cortex is proportional to the absolute error of a TEMPORAL MEMORY TRANSLATION CONSTANT.