***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Abstract Due to the high interindividual response variability following transcranial direct current stimulation ( tDCS ) , it is apparent that further research of the long‐lasting effects of the stimulation technique is required . We aim ed to investigate interindividual variability following anodal tDCS and cathodal tDCS in a large‐scale prospect i ve cross‐over study . Motor cortex physiology measurements were obtained using transcranial magnetic stimulation ( TMS ) in 59 healthy participants comparing motor‐evoked potential ( MEP ) magnitudes following two tDCS paradigms : 1 mA anodal tDCS for 13 min and 1 mA cathodal tDCS for 9 min . Analysis compared MEP changes over time for both polarities . Additionally , we applied hierarchical cluster analysis to assess the dynamics of poststimulation changes . Overall , anodal tDCS result ed in a significant increase in corticospinal excitability lasting for 40 min poststimulation , whereas cathodal tDCS did not alter corticospinal excitability . Cluster analysis revealed for cathodal tDCS both a cluster showing significant stable MEP reduction and a second cluster displaying MEP increase over time . Two diametrical clusters were also found for anodal tDCS . Regardless of polarity , individuals with MEP increase following stimulation showed steeper cortical recruitment curves compared to the clusters with decreased MEP magnitudes . The observed findings confirm a bidirectional modulation of corticospinal excitability following 1 mA tDCS in separate subgroups and the relationship to cortical recruitment BACKGROUND The brain-derived neurotrophic factor ( BDNF ) gene often shows a single nucleotide polymorphism that is thought to influence synaptic plasticity . It also affects the modulatory effects of repetitive transcranial magnetic stimulation ( rTMS ) on motor cortex excitability . OBJECTIVE This study investigated whether BDNF polymorphism influences the effect of  rTMS  on the motor recovery of patients with stroke . METHODS Forty-four patients ( mean age 53.8 years ) experiencing unilateral motor weakness after stroke were recruited .  rTMS was applied over the primary motor cortex of the affected hemisphere at 10 Hz with 1000 pulses/day for 10 days . Each patient 's motor functions were assessed using the Fugl-Meyer assessment ( FMA ) and the  box and block test ( BBT ) before , immediately after and 2 months after the intervention . BDNF genotyping was performed via PCR assays of whole blood sample s. The patients ' data were grouped and analysed into Val/Val and Met allele groups according to the presence or absence of the BDNF polymorphism . RESULTS Nine patients ( 20.5 % ) were classified into the Val/Val group , and thirty-seven patients ( 79.5 % ) were classified into the Met allele group . The patients ' baseline motor functions did not differ between the two groups . The FMA and BBT scores showed significant improvement immediately after and 2 months after rTMS in both groups . In addition , the time and groups were found to interact significantly , with the Val/Val group improving to a greater extent than the Met allele group in terms of their FMA and BBT scores . CONCLUSIONS The findings suggest that the BDNF gene polymorphism negatively influences the effect of  rTMS  on the motor recovery of upper extremities in stroke patients QUESTIONS Does the PEDro scale measure only one construct ie , the method ological quality of clinical trials ? What is the hierarchy of items of the PEDro scale from least to most adhered to ? Is there any effect of year of publication of trials on item adherence ? Are PEDro scale ordinal scores equivalent to interval data ? DESIGN Rasch analysis of two independent sample s of 100 clinical trials from the PEDro data base scored using the PEDro scale . RESULTS Both sample s of PEDro data showed fit to the Rasch model with no item misfit . The  PEDro scale item hierarchy was the same in both sample s , ranging from the most adhered to item r and om allocation , to the least adhered to item therapist blinding . There was no differential item functioning by year of publication . Original PEDro ordinal scores were highly correlated with transformed PEDro interval scores ( r = 0.99 ) . CONCLUSION The PEDro scale is a valid measure of the method ological quality of clinical trials . It is valid to sum PEDro scale item scores to obtain a total score that can be treated as interval level measurement and subjected to parametric statistical analysis CONTEXT Consecutive sessions of transcranial direct current stimulation ( tDCS ) over the primary motor cortex ( M1 ) may be a suitable therapy to treat chronic pain , as it can modulate neural activities in the stimulated and interconnected regions . OBJECTIVES The present study investigated the analgesic effect of five consecutive days of anodal/sham tDCS using subjective ( visual analog scale [ VAS ] ) and objective ( cortical excitability measured by transcranial magnetic stimulation [ TMS ] ) measurements . METHODS Patients with therapy-resistant chronic pain syndromes ( trigeminal neuralgia , poststroke pain syndrome , back pain , fibromyalgia ) participated . As this clinical trial was an exploratory study , statistical analyses implemented exploratory methods . Twelve patients , who underwent both anodal and sham tDCS , were analyzed using a crossover design . An additional nine patients had only anodal or sham stimulation . tDCS was applied over the h and area of the M1 for 20 minutes , at 1mA for five consecutive days , using a r and omized , double-blind design . Pain was assessed daily using a VAS rating for one month before , during , and one month post-stimulation . M1 excitability was determined using paired-pulse TMS . RESULTS Anodal tDCS led to a greater improvement in VAS ratings than sham tDCS , evident even three to four weeks post-treatment . Decreased intracortical inhibition was demonstrated after anodal stimulation , indicating changes in cortico-cortical excitability . No patient experienced severe adverse effects ; seven patients suffered from light headache after anodal and six after sham stimulation . CONCLUSION Results confirm that five daily sessions of tDCS over the h and area of the M1 can produce long-lasting pain relief in patients with chronic pain In this paper we demonstrate in the intact human the possibility of a non-invasive modulation of motor cortex excitability by the application of weak direct current through the scalp .  Excitability changes of up to 40 % , revealed by transcranial magnetic stimulation , were accomplished and lasted for several minutes after the end of current stimulation . Excitation could be achieved selectively by anodal stimulation , and inhibition by cathodal stimulation . By varying the current intensity and duration , the strength and duration of the after-effects could be controlled . The effects were probably induced by modification of membrane polarisation . Functional alterations related to post-tetanic potentiation , short-term potentiation and processes similar to postexcitatory central inhibition are the likely c and i date s for the excitability changes after the end of stimulation . Transcranial electrical stimulation using weak current may thus be a promising tool to modulate cerebral excitability in a non-invasive , painless , reversible , selective and focal way 
    Output:
    
The results of this systematic review appear to indicate that statistical cluster analysis techniques are effective in identifying subgroups of individuals based on response patterns to non-invasive brain stimulation .
This systematic review also reports a lack of consensus amongst research ers on the most effective subgrouping technique and the criteria used to determine whether an individual is categorised as a responder or a non-responder .