A model containing only neurons may be too simplistic - glial cells also seem to modulate cognition in ways that haven't yet been fully elucidated. Then you als

A model containing only neurons may be too simplistic - glial cells also seem to modulate cognition in ways that haven't yet been fully elucidated. Then you also have rather more asymmetric synaptic behaviours such as volume transmission, where the neurotransmitter is diffused across a less well-defined area, rather than being kept neatly within a shared synaptic cleft.