Auditory cortex supports verbal working memory capacity

Abstract

Working memory (WM) is a fundamental construct of human cognition that predicts important faculties such as language abilities and scholastic achievement. The neural basis of auditory WM is thought to reflect a distributed brain network consisting of canonical memory and central executive brain regions including frontal lobe, prefrontal areas, and hippocampus. Yet, the role of auditory (sensory) cortex in supporting active memory representations remains controversial. Here, we recorded neuroelectric activity via EEG as listeners actively performed an auditory version of the Sternberg memory task. Memory load was taxed by parametrically manipulating the number of auditory tokens (letter sounds) held in memory. Source analysis of scalp potentials showed that sustained neural activity maintained in auditory cortex (AC) prior to memory retrieval closely scaled with behavioral performance. Brain-behavior correlations revealed lateralized modulations in left (but not right) AC predicted individual differences in auditory WM capacity. Our findings confirm a prominent role of auditory cortex, traditionally viewed as a sensory-perceptual processor, in actively maintaining memory traces and dictating individual differences in behavioral WM limits.

Information flows from hippocampus to auditory cortex during replay of verbal working memory items

“…Compared to encoding, maintenance showed enhanced PLV in the theta range between hippocampal LFP and cortical ECoG (PLV = 0.4 in contact C3, permutation test p<0.05, Fig 2 f ). PLV in the [4-8] Hz theta range increased significantly with several contacts over auditory cortex (permutation test p<0.05, Fig 2 g ). This speaks for a functional coupling between auditory cortex and hippocampus mediated by synchronized oscillations [26].…”

“…The reversal of ΔGranger appeared in all 15 participants individually ( Fig 4d ). We averaged ΔGranger for each participant in the [4-8] Hz theta frequency range. The ΔGranger between hippocampus and auditory cortex, was negative during encoding and was positive during maintenance in the (p = 4.1e-10, paired permutation test).…”

“…Maintaining content in WM requires collaboration within a widespread network of brain regions. The anatomical basis of WM was shown noninvasively with EEG / MEG (3)(4)(5)(6)(7)(8)(9) and invasively with intracranial EEG (10)(11)(12)(13)(14)(15)(16)(17)(18)(19) and single unit recordings (19)(20)(21)(22).…”

“…Maintaining content in WM requires communication within a widespread network of brain regions. The anatomical basis of WM was shown noninvasively with EEG / MEG [3][4][5][6][7][8][9][10] and invasively with intracranial local field potentials (LFP) [11][12][13][14][15][16][17][18][19][20][21] and single unit recordings [19,[21][22][23][24].…”

“…The phase difference between the two signals indexes the coherence between each electrode pair and is expressed as the PLV. The PLV ranges between 0 and 1, with values approaching 1 if the two signals show a constant phase relationship over all trials.In our description of EEG frequency bands, we used theta (4-8 Hz), alpha(8)(9)(10)(11)(12) Hz), beta (12-24 Hz) and gamma (> 40 Hz), while the exact frequencies may differ in individual participants.…”