Auditory cortex supports verbal working memory capacity

Abstract

Working memory (WM) is a fundamental construct of human cognition. 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 and hippocampus. Yet, the role of auditory (sensory) cortex in supporting active memory representations remains controversial. Here, we recorded neuroelectric activity via electroencephalogram 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 that lateralized modulations in left (but not right) AC were predictive of individual differences in auditory WM capacity. Our findings confirm a prominent role of AC, traditionally viewed as a sensory-perceptual processor, in actively maintaining memory traces and dictating individual differences in behavioral WM limits.

Fig. 1:. Auditory WM stimulus paradigm and behavioral data.

(a) Listeners heard between 2 and 8 characters (“Memory set”) presented auditorily. Following a retention period, they indicated whether a “Probe” occurred in the prior memory set. Shown here is a “no match” trial. (b-c) Behavioral accuracy for probe recall decreases and response times increase with additional memory load. (d) Working memory capacity (K) increases for small set sizes but saturates >4 items, above listeners’ WM capacity limits. errorbars =± 1 s.e.m.

Fig. 2:. Scalp ERPs reveal load-dependent modulations in sustained neural activity during WM maintenance.

(a) ERP time courses at central scalp locations (mean of electrodes C1/2, Cz, CP1/2, CPz; baseline = [−4400 to −3700 ms]). Transient peaks during “encoding” reflect auditory responses to final stimulus tokens in the memory set. Sustained activity is modulated in the 3 sec maintenance interval during memory retention (highlighted segment) and is stronger for low (2/4) vs. high (6/8) load (inset). errorbars =± 1 s.e.m.

Fig. 3:. Sustained neural activity maintained in AC predicts behavioral auditory WM capacity.

(a) T-stat map contrasting low (2/4) vs. high (6/8) CLARA source activation maps (P<0.05 masked, uncorrected). Functional data are overlaid on the MNI brain template. WM load is distinguished in bilateral Sylvian fissure. (b-c) AC amplitudes vary with set size but load-related changes in left (but not right) AC mirror the pattern observed in scalp EEG (cf. Fig. 2a) (d-e) Maximum behavioral WM capacity (K_{load 8}) is predicted by AC activity in left hemisphere; individuals with larger changes in source amplitudes with set size have larger WM capacity. No brain-behavior relation is observed in right hemisphere. Dashed lines=95% CI; solid lines, significant correlation; dotted lines, n.s. correlation. *P<0.05. errorbars =± 1 s.e.m.; AC, auditory cortex.