Direct brain recordings reveal prefrontal cortex dynamics of memory development
Elizabeth Johnson1,2, Qin Yin2, Lingfei Tang2, Eishi Asano2, Noa Ofen2; 1University of California, Berkeley, 2Wayne State University
Prevailing fMRI evidence points to the role of protracted prefrontal cortex maturation in the development of memory function. Until recently, however, it was not possible to detail the precise timing of frontal activity in the developing brain. We provide rare insight from 17 children and adolescents (6.2-19.4 years) undergoing direct cortical monitoring (ECoG), which yields data with unprecedented spatiotemporal precision in the study of neurocognitive development. Subjects encoded pictures of scenes in preparation for a recognition test. We examined the temporal propagation of frontal activity during encoding as a function of subsequent memory, and the large sample size allowed us to further examine individual differences. The multitaper time-frequency spectrum was calculated between 30-250 Hz in all lateral frontal channels (n = 447) and the 3-s encoding power segments were z-scored on a 300-ms pre-stimulus baseline via statistical bootstrapping. Outputs were analyzed per-trial on the individual level, and then modeled on the group level using linear mixed-effects models and ANCOVA. Results provide initial evidence that the developing frontal cortex is active within 1 s from scene onset, and that earlier precentral, middle frontal, and superior frontal gyrus activation predicts greater memory accuracy. Furthermore, sub-second deviations in the timing and directionality of dynamic activity flow between precentral and inferior and middle frontal gyri dictate whether scenes are subsequently remembered or forgotten. Finally, the lack of age-related variability challenges prevailing theories of memory development, and instead shows that even young children exhibit memory-relevant patterns of frontal activity, comparable to adolescents.
Topic Area: LONG-TERM MEMORY: Development & aging