Figure 1.

Random and structured patterns of local connectivity. (A) Simplified schematic of the inputs to a medium spiny neuron in the striatum. There is a clear structure to the targeting of different types of inputs. Such multi-type structure is reviewed extensively elsewhere and will not be discussed further. (B) Generalized CNS neuron (e.g., cortical pyramidal cell) in which inputs of one type only are shown. Within that type, different input cohorts are defined solely on the basis of their activation histories: each cohort (A or B, among many) has correlated activity whereas different cohorts are uncorrelated. In this example, synapses from three input cohorts are distributed randomly throughout the dendritic field. This is a Braitenberg network. (C) Example of between-branch selectivity. Three cohorts have equal access to the leftmost dendrite but only one actually synapses with it. (D) Example of within-branch structure. Synapses from each cohort are spatially clustered.