DISCONNECTION OF INTRACORTICAL SYNAPTIC LINKAGES DISRUPTS SYNCHRONIZATION OF A SLOW OSCILLATION

The intracortical synaptic linkages underlying the synchronization of a recently described slow (<1 Hz) oscillation (Steriade et al., 1993b, c) were investigated in anesthetized cats by means of multisite extra- and intracellular recordings, including dual impalements, from rostra l and caudal sites in the association cortical suprasylvian and margin al gyri, before and after reversible lidocaine inactivation or transec tions in the middle suprasylvian gyrus, Stimulus-evoked responses reve aled that the rostral and caudal suprasylvian foci are reciprocally co nnected, with a preference for posterior-to-anterior responses. Lidoca ine infusion between the stimulating and recording sites disrupted the intracortical synaptic linkage, while leaving unaffected the response s at the sites close to the stimulating electrodes. The high coherence between slowly oscillating field potentials and intracellular activit ies recorded from anterior and posterior suprasylvian foci was lost af ter reversible inactivation or transections in the middle suprasylvian gyrus, whereas the synchrony between adjacent foci within the anterio r or posterior areas was preserved, Two to four hours after inactivati on or transection the synchrony between all channels was totally or pa rtially recovered, We introduced the synchrony coefficient (SyCo) and calculated the SyCo for closely located and distant sites. Lidocaine i nfusion or transection did not affect the SyCo between leads placed on the same site, but significantly (60%) decreased the SyCo between cha nnels separated by the functionally inactivated or transected sector. Our results demonstrate that pathways within or beneath the suprasylvi an gyrus sustain the synchronization of the slow oscillation between c ortical sites, As the loss of long-range coherence was not permanent, intergyral paths and/or corticothalamocortical loops may exert compens atory functions after the disconnection of intrasuprasylvian synaptic linkages.