Neurofeedback is attracting renewed interest as a method to self-regulate one's own brain activity to directly alter the underlying neural mechanisms of cognition and behavior. It not only promises ...new avenues as a method for cognitive enhancement in healthy subjects, but also as a therapeutic tool. In the current article, we present a review tutorial discussing key aspects relevant to the development of electroencephalography (EEG) neurofeedback studies. In addition, the putative mechanisms underlying neurofeedback learning are considered. We highlight both aspects relevant for the practical application of neurofeedback as well as rather theoretical considerations related to the development of new generation protocols. Important characteristics regarding the set-up of a neurofeedback protocol are outlined in a step-by-step way. All these practical and theoretical considerations are illustrated based on a protocol and results of a frontal-midline theta up-regulation training for the improvement of executive functions. Not least, assessment criteria for the validation of neurofeedback studies as well as general guidelines for the evaluation of training efficacy are discussed.
•Noninvasive neurostimulation can potentially improve negative symptoms.•The effect of lateral prefrontal stimulation on active behavior suggests a causal role.•Moderator variables such as intensity ...of stimulation and duration of illness are relevant.
Negative symptoms in schizophrenia concern a clinically relevant reduction of goal-directed behavior that strongly and negatively impacts daily functioning. Existing treatments are of marginal effect and novel approaches are needed. Noninvasive neurostimulation by means of repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are novel approaches that may hold promise.
To provide a quantitative integration of the published evidence regarding effects of rTMS and tDCS over the frontal cortex on negative symptoms, including an analysis of effects of sham stimulation.
Meta-analysis was applied, using a random effects model, to calculate mean weighted effect sizes (Cohen's d). Heterogeneity was assessed by using Cochrans Q and I2 tests.
For rTMS treatment, the mean weighted effect size compared to sham stimulation was 0.64 (0.32–0.96; k = 22, total N = 827). Studies with younger participants showed stronger effects as compared to studies with older participants. For tDCS studies a mean weighted effect size of 0.50 (−0.07 to 1.07; k = 5, total N = 134) was found. For all frontal noninvasive neurostimulation studies together (i.e., TMS and tDCS studies combined) active stimulation was superior to sham, the mean weighted effect size was 0.61 (24 studies, 27 comparisons, 95% confidence interval 0.33–0.89; total N = 961). Sham rTMS (baseline - posttreatment comparison) showed a significant improvement of negative symptoms, d = 0.31 (0.09–0.52; k = 16, total N = 333). Whereas previous meta-analyses were underpowered, our meta-analysis had a power of 0.87 to detect a small effect.
The available evidence indicates that noninvasive prefrontal neurostimulation can improve negative symptoms. This finding suggests a causal role for the lateral frontal cortex in self-initiated goal-directed behavior. The evidence is stronger for rTMS than for tDCS, although this may be due to the small number of studies as yet with tDCS. More research is needed to establish moderator variables that may affect response to neurostimulation and to optimize treatment parameters in order to achieve stable and durable (and thus clinically relevant) effects.
Response inhibition paradigms, as for example stop signal and go/no-go tasks, are often used to study cognitive control processes. Because of the apparent demand to stop a motor reaction, the ...electrophysiological responses evoked by stop and no-go trials have sometimes likewise been interpreted as indicators of inhibitory processes. Recent research, however, suggests a richer conceptual background. Evidence denotes an association of a frontal-midline N200/theta oscillations with premotor cognitive processes such as conflict monitoring or response program updating, and an anterior P300/delta oscillations with response-related, evaluative processing stages, probably the evaluation of motor inhibition. However, the data are still insufficient to unambiguously relate these electroencephalographic measures to specific inhibitory functions. Beta band activity only recently has become a focus of attention in this task context because of its association with the motor system and regions involved in inhibitory control. Its functional role in response inhibition tasks needs further exploration though. Hence, as things stand, any deduction of differences regarding actual inhibitory capabilities or loads between subject groups or conditions based on electroencephalographic measures has to be treated with caution.
► EEG studies of stop signal and go/no-go tasks are reviewed. ► N200/frontal-midline theta seem to be associated with premotor processes. ► P300/delta oscillations reflect response-related, evaluative processing stages. ► EEG-indicators of proper inhibitory functions are undetermined.
Conflict and inhibition are considered to exert strong influences on the neurophysiological N200 and P300 brain responses as evoked in go/nogo and stop-signal tasks. In order to separate their ...underlying neural and functional mechanisms, the current experiment manipulated both conflict and inhibition. To do so, the go/nogo and stop-signal tasks were merged into one paradigm. Conflict was manipulated by varying go-trial frequencies across blocks (75% vs. 25%). Motor inhibition was manipulated by using go, nogo and stop trials each representing a different load of inhibition. Event-related potentials (ERPs) as well as current density reconstructions (CDRs) of fifteen healthy participants were analyzed. Overall, infrequent trials evoked significantly more pronounced N200s than frequent trials. The P300 predominantly revealed significant variations between trial types (go, nogo, stop). Estimated source activations of the MCC and the IFC supported the ERP results; N200-related effects were revealed in both regions, whereas the condition-specific variations of the P300 were only observed in the IFC. The results indicate that the N200 primarily reflects conflict-related effects whereas the P300 predominantly represents motor inhibition.
Frontal-midline (fm) theta oscillations as measured via the electroencephalogram (EEG) have been suggested as neural "working language" of executive functioning. Their power has been shown to ...increase when cognitive processing or task performance is enhanced. Thus, the question arises whether learning to increase fm-theta amplitudes would functionally impact the behavioral performance in tasks probing executive functions (EFs). Here, the effects of neurofeedback (NF), a learning method to self-up-regulate fm-theta over fm electrodes, on the four most representative EFs, memory updating, set shifting, conflict monitoring, and motor inhibition are presented. Before beginning and after completing an individualized, eight-session gap-spaced NF intervention, the three-back, letter/number task-switching, Stroop, and stop-signal tasks were tested while measuring the EEG. Self-determined up-regulation of fm-theta and its putative role for executive functioning were compared to an active control group, the so-called pseudo-neurofeedback group. Task-related fm-theta activity after training differed significantly between groups. More importantly, though, after NF significantly enhanced behavioral performance was observed. The training group showed higher accuracy scores in the three-back task and reduced mixing and shifting costs in letter/number task-switching. However, this specific protocol type did not affect performance in tasks probing conflict monitoring and motor inhibition. Thus, our results suggest a modulation of proactive but not reactive mechanisms of cognitive control. Furthermore, task-related EEG changes show a distinct pattern for fm-theta after training between the NF and the pseudo-neurofeedback group, which indicates that NF training indeed tackles EFs-networks. In sum, the modulation of fm-theta via NF may serve as potent treatment approach for executive dysfunctions.
Humans differ in their ability to learn how to control their own brain activity by neurofeedback. However, neural mechanisms underlying these inter-individual differences, which may determine ...training success and associated cognitive enhancement, are not well-understood. Here, it is asked whether neurofeedback success of frontal-midline (fm) theta, an oscillation related to higher cognitive functions, could be predicted by the morphology of brain structures known to be critically involved in fm-theta generation. Nineteen young, right-handed participants underwent magnetic resonance imaging of T1-weighted brain images, and took part in an individualized, eight-session neurofeedback training in order to learn how to enhance activity in their fm-theta frequency band. Initial training success, measured at the second training session, was correlated with the final outcome measure. We found that the inferior, superior, and middle frontal cortices were not associated with training success. However, volume of the midcingulate cortex as well as volume and concentration of the underlying white matter structures act as predictor variables for the general responsiveness to training. These findings suggest a neuroanatomical foundation for the ability to learn to control one's own brain activity.
Impairments in executive functions (EFs) are common across disorders and can greatly affect daily functioning. Frontal-midline (FM) theta neurofeedback (NF) has been shown effective in enhancing EFs ...in healthy adults, prompting interest in exploring its potential as an alternative treatment for EFs in (sub)clinical samples. This study aims to determine the effects of FM theta NF on EFs in a sample of 58 adults (aged 20-60 years) with pronounced subjective EF complaints in daily life. Using a pre/post/follow-up design with a sham NF group, the present study assessed upregulation of FM theta in an eight-session individualized FM theta NF training and its immediate and long-term transfer effects on objective and subjective measures of EFs. These included behavioral performance on EF tasks assessing working memory updating (N-back task), set-shifting (Switching task), conflict monitoring (Stroop task), and response inhibition (Stop-signal task), as well as FM theta power during these tasks, and subjective EFs in daily life (BRIEF-A). The results indicate that there are only differences in FM theta self-upregulation between the NF group and sham group when non-responders are excluded from the analysis. Regarding behavioral transfer effects, NF-specific improvements are found in working memory updating reaction time (RT) and conflict monitoring RT variability at 6-month follow-up, but not immediately after the NF training. The effects on FM theta power during the EF tasks and subjective changes in EFs in daily life were not specific to the NF training. As a next step, research should identify the best predictors to stratify NF training, as well as explore ways to improve NF responsiveness, for instance by increasing neuroplasticity.
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