Fig. 1

Formation and reactivation of inter-postsynaptic functional LINKs. a The illustration shows functional LINK formation between two postsynaptic membranes (postsynapses or dendritic spines) B and D when they are simultaneously activated when two stimuli are associated. The functional LINK is reversible, stabilizable and its formation is a function of the simultaneous activation of postsynapses B and D. A and C are corresponding presynaptic terminals. b At a later time, when one of the stimuli arrives at postsynapse B through synapse A–B, functional LINK B–D is re-activated, resulting in the activation of postsynaptic membrane D. This induces a unit of internal sensation of activity arriving from presynaptic terminal C. The reactivation of the functional LINK is a function of arrival of activity at one of the postsynaptic terminals. c Two abutted synapses are shown with their presynaptic and postsynaptic terminal membranes in lipid bilayers. Note that the postsynaptic membranes are separated by extracellular matrix space. d The formed inter-postsynaptic functional LINK is shown in red. Both direct membrane contact by excluding inter-membrane hydrophilic region and reversible partial membrane hemifusion are common mechanisms (Figure modified from Vadakkan 2010)