Does non-invasive brain stimulation applied over the dorsolateral prefrontal cortex non-specifically influence mood and emotional processing in healthy individuals?

Marine Mondino,François Thiffault,Shirley Fecteau

doi:10.3389/fncel.2015.00399

Abstract

The dorsolateral prefrontal cortex (DLPFC) is often targeted with non-invasive brain stimulation (NIBS) to modulate in vivo human behaviors. This brain region plays a key role in mood, emotional processing, and attentional processing of emotional information. In this article, we ask the question: when we target the DLPFC with NIBS, do we modulate these processes altogether, non-specifically, or can we modulate them selectively? We thus review articles investigating the effects of NIBS applied over the DLPFC on mood, emotional processing, and attentional processing of emotional stimuli in healthy subjects. We discuss that NIBS over the DLPFC can modulate emotional processing and attentional processing of emotional stimuli, without specifically influencing mood. Indeed, there seems to be a lack of evidence that NIBS over the DLPFC influences mood in healthy individuals. Finally, there appears to be a hemispheric lateralization: when applied over the left DLPFC, NIBS improved processing of positive stimuli and reduced selective attention for stimuli expressing anger, whereas when applied over the right DLPFC, it increased selective attention for stimuli expressing anger.

Highlights

Non-invasive brain stimulation techniques (NIBS) such as repetitive transcranial magnetic stimulation and transcranial direct current stimulation can modulate human brain activity and connectivity (Shafi et al, 2012) and selectively improve or disrupt behaviors (Bikson and Rahman, 2013)
Hemispherical specialization of emotional processing has been proposed: activation in the left dorsolateral prefrontal cortex (DLPFC) has been associated with positive mood and processing positive stimuli, whereas activation in the right DLPFC has NIBS effects on mood and emotion been linked to negative mood and processing negative stimuli (Canli et al, 1998)
We reviewed here studies investigating the effects of NIBS applied over the DLPFC on mood, emotional processing and attentional processing of emotional information in healthy individuals

Summary

Introduction

Non-invasive brain stimulation techniques (NIBS) such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) can modulate human brain activity and connectivity (Shafi et al, 2012) and selectively improve or disrupt behaviors (Bikson and Rahman, 2013). Schaller et al (2011) found elevated mood after delivering nine sessions of 25 Hz rTMS over the left DLPFC when measured with the Beck Depression Inventory (BDI), but not with a 6-item VAS To these studies, others reported no significant mood change with high-frequency rTMS over the DLPFC. Most studies reported that NIBS does not significantly influence mood in healthy subjects Those reporting positive findings indicated a hemispheric lateralization: targeting the left DLPFC induced both negative and positive mood, whereas targeting the right DLPFC elevated mood. Studies applied NIBS over the DLPFC of healthy individuals to investigate emotional processing, especially perception of valence, identification of facial expressions, and retrieval of emotional information (Table 1B). For identification of facial expressions, Nitsche et al (2012) reported that subjects were faster at identifying faces expressing positive and negative emotions during anodal or cathodal tDCS over the left DLPFC, with greater effect during anodal tDCS and positive stimuli. Conson et al (2015) found that healthy men, but not women, were faster at recognizing fearful faces after receiving anodal and cathodal tDCS over the right and left DLPFC, respectively

Study design

Recognition of facial expressions task

Findings

Discussion