Cognitive N140 electrogenesis and concomitant 40 Hz synchronization in mid-dorsolateral prefrontal cortex (area 46) identified in non-averaged human brain potentials

The mid-dorsolateral prefrontal area 46 has working memory functions for pu tting current cognitive processing into context and for updating relevant i nformation on a trial-by-trial basis. Using non-averaged human brain respon ses to a target finger stimulus attended by the subject, we identified the cognitive prefrontal N140 electrogenesis with the Z method which numericall y assesses the detailed consistency between scalp topographies of a ny sing le response and a grand average template. The cognitive N140 was present be tween 100 and 180 ms at the scalp contralateral to the attended target fing er stimulus. Control responses to physically identical finger stimuli that were ignored by the subject did not elicit a prefrontal N140. in brain mapp ing the N140 focus was located 30-80 mm from scalp midline, and 50-60 mm in front of the vertex (Cz) coronal plane of the head. The data were consiste nt with recently disclosed anatomical locations of area 46 and they further document its interindividual variations in brain-to-scalp relationship. N1 40 is thought to manifest cortico-cortical activation from the posterior pa rietal area 7b which generates the cognitive P100 electrogenesis that prece des N140 in the target response. At the prefrontal site, the non-averaged E EG showed desynchronized 40 Hz oscillations, but these became transiently p hase-locked in conjunction with the cognitive N140 excitatory effect. This seems in line with the Traub model suggesting that excitation of certain co rtical inhibitory interneurons generates doublet firings which will pace th e spiking of pyramidal neurons so as to promote synchronization at about 40 Hz. These results complement our recent finding that P300 inhibition conve rsely disrupts on-going 40 Hz phase-locking ('binding'). Considering the ma rked trial-to-trial variations in timing of the cortical cognitive processe s, such physiological relationships between target response components and 40 Hz dynamics could only be uncovered by studying nonaveraged single respo nses. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.