Effects of left dlPFC modulation on social cognitive processes following food sampling.

BACKGROUND: The dorsolateral prefrontal cortex (dlPFC) plays a central role in the inhibition of eating, but also the modulation of conscious thought processes that might precede, accompany or follow initial food tasting. The latter might be particularly important to the extent that post-tasting cognitions may drive prolonged eating beyond the satiety point. However, we know very little about the effect of the dlPFC on conation following initial food sampling. This investigation compared the effects of dlPFC attenuation using repetitive transcranial magnetic stimulation (rTMS) on social cognition following (Study 1) and prior to (Study 2) a food consumption opportunity. METHODS: In Study 1, participants (N = 21; Mage = 21 years) were randomized to active or sham continuous theta-burst stimulation (cTBS; an inhibitory variant of rTMS) targeting the left dlPFC followed by an interference task. Participants subsequently completed measures of attitudes, norms and perceived control following a mock taste test. In Study 2, a second sample of right handed participants (N = 37; Mage = 21 years) were assigned to active or sham cTBS, followed by an interference task and two measures of attitudes (implicit and explicit), both assessed prior to the same taste test paradigm. RESULTS: In Study 1, findings revealed a reliable effect of cTBS on post-tasting attitudes (t(1,19) = 3.055, p = .007; d = 1.34), such that attitudes towards calorie dense snack foods were significantly more positive following active stimulation than following sham stimulation. Similar effects were found for social norms (t(1,19) = 3.024, p = .007, d = 1.31) and perceived control (t(1,20) = 19.247, p < .001, d = 0.50). In Study 2, no effects of cTBS were observed on pre-consumption attitudes, despite reliable effects on interference scores and subsequent consumption. CONCLUSIONS: The left dlPFC may selectively modulate facilitative social cognition following initial food sampling (but not pre-consumption).

Mind wandering on command.

Three experiments (N = 336) examined whether participants can systematically adjust levels of mind wandering on command. Participants performed four blocks of the metronome response task (MRT) in which they pressed a spacebar in sync with a steady audio tone. Levels of spontaneous and deliberate mind wandering were measured using intermittent thought probes. Performance was indexed with MRT response time variability and omission errors. Each block started with instructions to mind wander either 20, 40, 60, or 80% of the time. Analysis was primarily conducted using linear mixed effects models. We found that mind wandering (spontaneous and deliberate), response time variability, and omission errors increased progressively with instructions to mind wander more and that these instruction-related changes were larger for deliberate than spontaneous mind wandering (Experiments 1-3). This pattern held regardless of whether participants' eyes were open or shut (Experiment 2). Relative to a control group receiving no commands to mind wander, instructing people to mind wander 60 or 80% of the time led to more deliberate mind wandering, and strikingly, asking people to mind wander 20% of the time led to less spontaneous mind wandering (Experiment 3). Our results suggest that individuals can titrate mind wandering experiences to roughly match instructed levels indicating that mind wandering can be manipulated through simple instructions. However, other features of the data suggest that such titration is effortful and may come with a cost to performance.

Effects of prefrontal theta burst stimulation on neuronal activity and subsequent eating behavior: an interleaved rTMS and fNIRS study.

The dorsolateral prefrontal cortex (dlPFC) and dorsomedial prefrontal cortex (dmPFC) are both important nodes for self-control and decision-making but through separable processes (cognitive control vs evaluative processing). This study aimed to examine the effects of excitatory brain stimulation [intermittent theta burst stimulation (iTBS)] targeting the dlPFC and dmPFC on eating behavior. iTBS was hypothesized to decrease consumption of appetitive snack foods, via enhanced interference control for dlPFC stimulation and reduced delay discounting (DD) for dmPFC stimulation. Using a single-blinded, between-subjects design, participants (N = 43) were randomly assigned to one of three conditions: (i) iTBS targeting the left dlPFC, (ii) iTBS targeting bilateral dmPFC or (iii) sham. Participants then completed two cognitive tasks (DD and Flanker), followed by a bogus taste test. Functional near-infrared spectroscopy imaging revealed that increases in the medial prefrontal cortex activity were evident in the dmPFC stimulation group during the DD task; likewise, a neural efficiency effect was observed in the dlPFC stimulation group during the Flanker. Gender significantly moderated during the taste test, with females in the dmPFC showing paradoxical increases in food consumption compared to sham. Findings suggest that amplification of evaluative processing may facilitate eating indulgence when preponderant social cues are permissive and food is appetitive.

Examining the relationships among adolescent health behaviours, prefrontal function, and academic achievement using fNIRS.

Several adolescent health behaviours have been hypothesized to improve academic performance via their beneficial impact on cognitive control and functional aspects of the prefrontal cortex (PFC). The primary objective of this study is to examine the association between lifestyle behaviours and academic performance in a sample of adolescents, and to examine the extent to which activity within the PFC and behavioural indices of inhibition may mediate this relationship. Sixty-seven adolescents underwent two study sessions five days apart. Sleep and physical activity were measured using wrist-mounted accelerometry; eating habits, substance use and academic achievement were measured by self-report. Prefrontal function was quantified by Multi-Source Interference Task (MSIT) performance, and task-related activity via functional near-infrared spectroscopy (fNIRS). Higher levels of physical activity predicted higher MSIT accuracy scores (ß = .321, ρ = 0.019) as well as greater activation within the right dlPFC (b = .008, SE = .004, ρ = .0322). Frequency of fast-food consumption and substance use were negatively associated with MSIT accuracy scores (ß = -0.307, ρ = .023) and Math grades (b = -3.702, SE = 1.563, ρ = .022), respectively. Overall, the results of this study highlight the importance of lifestyle behaviours as predictors of prefrontal function and academic achievement in youth.

Contextual cues as modifiers of cTBS effects on indulgent eating.

BACKGROUND: Prior studies have found that continuous theta burst stimulation (cTBS) targeting the left dlPFC results in reliable increases in consumption of calorie-dense food items. However, it is not known to what extent such effects are modified by cues in the immediate eating environment. Tempting environments (i.e., those saturated with appetitive eating cues) may lead to more reliance on cognitive control networks involving the dlPFC, thereby enhancing cTBS effects on indulgent eating. OBJECTIVE/HYPOTHESIS: The objective was to examine the extent to which cTBS effects on indulgent eating would be modified by contextual cues. It was hypothesized that cTBS effects would be stronger in the presence of facilitating cues. METHODS: Using a single-blinded between-subjects factorial design, 107 TMS-naïve adults were randomly assigned to one of four conditions: 1) active cTBS + facilitating cues, 2) sham cTBS + facilitating cues, 3) active cTBS + inhibiting cues, 4) sham cTBS + inhibiting cues. Following stimulation participants completed a flanker paradigm and a taste test during which quantity consumed was assessed surreptitiously. RESULTS: Findings revealed a significant interaction between stimulation and cue type (F(1,102) = 6.235, p = .014), such that cTBS resulted in increased food consumption (compared to sham) in the presence of the facilitating cue but not in the presence of the inhibiting cue. Moderated mediational analyses showed selective mediation of cTBS effects on consumption through cTBS attenuation of flanker interference scores. CONCLUSIONS: The effects of cTBS on indulgent eating are strengthened in the presence of facilitating cues. Methodologically speaking, facilitating cues may be a functional prerequisite for exploring cTBS effects on eating in the laboratory. Substantively, the findings also suggest that facilitating cues in the eating environment may amplify counter-intentional food indulgence in everyday life via cognitive control failure.

The effects of theta burst stimulation (TBS) targeting the prefrontal cortex on executive functioning: A systematic review and meta-analysis.

Theta burst stimulation (TBS) is a highly efficient repetitive transcranial magnetic stimulation (rTMS) variant employed in experimental and clinical treatment paradigms. Despite widespread usage of TBS targeting the prefrontal cortex (PFC), there has been no systematic review of the evidence linking TBS protocols to changes in task performance on common measures of prefrontal function in general, and executive functions specifically. A systematic review of the literature was conducted using PsycINFO, PubMed, Web of Science and Scopus databases to identify articles examining the effects of TBS targeting the PFC on executive function task performance. Both the up-regulating (intermittent theta burst stimulation; iTBS) and down-regulating (continuous theta burst stimulation; cTBS) variants of TBS were considered. 32 (29 cTBS; 8 iTBS) studies met the inclusion criteria. Participants (n = 759; 51.41% female) were primarily young adults (Mage = 26), with one study examining the effects of cTBS and iTBS in older adults. Results from individual studies were converted to Hedge's g and random-effects models were used to estimate the overall effect size for each protocol. Age, biological sex, and control methodology were examined as potential moderators of the cTBS effect on executive function test performance. Findings indicated a- reliable attentuating effect of cTBS on executive function task performance (g = -.244, Z = -5.920, p < .001); this effect was relatively uniform across included studies (Q= 24.178, p = .838, I2 = 0). Although no significant moderators of the cTBS effect were identified, laterality sub analyses indicated that the magnitude of the effect was significantly higher (Mdiff = .213, Zdiff = 2.546, p = .011) for left-sided (g = -.358, Z = -5.816, p < .001) relative to right-sided (g = -.145, Z = -2.552, p = .011) PFC stimulation. A systematic review of iTBS studies revealed variability in reliability of effects though most were in the theorized direction. TBS protocols appear to be effective in modulating prefrontal cortical excitability in previously theorized directions.