Effects of 10 Hz rTMS on the neural efficiency of working memory

Abstract

Working memory (WM) has been described as short-term retention of information that is no longer accessible in the environment, and the manipulation of this information for subsequent use in guiding behavior. WM is viewed as a cognitive process underlying higher-order cognitive functions. Evidence supports a critical role for PFC in mediating WM performance. Studies show psychomotor processing speed and accuracy account for considerable variance in neural efficiency (Ne). This study compared the relative effects of active and sham 10 Hz rTMS applied to dorsolateral prefrontal cortex (DLPFC) on indices of Ne in healthy participants performing a WM paradigm that models the association between WM load and task behavior [Sternberg, S. High-speed scanning in human memory. Science, 153, 652-654, 1966]. Previous studies identified a relationship between diminished Ne and impaired WM across a broad array of clinical disorders. In the present study, the authors predicted there would be a main effect of stimulation group (STM) on accuracy (SCR) and processing speed (RT), hence, Ne. We observed a main effect of STM for RT without an effect on SCR; even so, there was a robust effect of STM on Ne.

Figures

Figure 1

Experimental design.

Figure 2

Comparative effects of active and sham 10 Hz rTMS on working memory reaction time. Left-side sequence: Pre-10 Hz rTMS RT*; Post-10 Hz rTMS RT; RT difference. Right-side sequence: RT difference; Pre-10 Hz rTMS RT*; Post-10 Hz rTMS RT. Compared with sham, the group treated with active 10 Hz rTMS applied to DLPFC 10 sec before onset experienced a 219-msec enhancement of RT.

Figure 3

Lack of effect of 10 Hz rTMS on accuracy within or between subjects. The difference in accuracy within and between groups pre- and poststimulation was not significant.