title: Physiological and behavioral effects of β-tACS on brain self-regulation in chronic stroke.
abstract: Unlike in healthy controls, sensorimotor β-desynchronization (β-ERD) is compromised in stroke patients, i.e., the more severe the patient's motor impairment, the less β-ERD. This, in turn, provides a target substrate for therapeutic brain self-regulation and neurofeedback.
  
  
  
  Transcranial alternating current stimulation (tACS) has been shown to modulate brain oscillations during and after stimulation, and may thus facilitate brain self-regulation during neurofeedback interventions.
  
  
  
  Twenty severely impaired, chronic stroke patients performed kinesthetic motor-imagery while a brain-robot interface transformed β-ERD (17-23 Hz) of the ipsilesional sensorimotor cortex into opening of the paralyzed hand by a robotic orthosis. In a parallel group design, β-tACS (20 Hz, 1.1 mA peak-to-peak amplitude) was applied to the lesioned motor cortex either continuously (c-tACS) before or intermittently (i-tACS) during the intervention. Physiological effects of β-tACS were studied using electroencephalography. The patients' ability for brain self-regulation was captured by neurofeedback performance metrics.
  
  
  
  i-tACS - but not c-tACS - improved the classification accuracy of the neurofeedback intervention in comparison to baseline. This effect was mediated via the increased specificity of the classification, i.e., reduced variance of resting oscillations. Neither i-tACS nor c-tACS had aftereffects following the stimulation period.
  
  
  
  β-tACS may constitute an adjunct neuromodulation technique during neurofeedback-based interventions for stroke rehabilitation.
authors.affiliation: Division of Functional and Restorative Neurosurgery, and Centre for Integrative Neuroscience, University of Tuebingen, Germany. Electronic address: georgios.naros@med.uni-tuebingen.de.
authors.forename: Georgios
authors.initials: G
authors.lastname: Naros
authors.affiliation: Division of Functional and Restorative Neurosurgery, and Centre for Integrative Neuroscience, University of Tuebingen, Germany. Electronic address: alireza.gharabaghi@uni-tuebingen.de.
authors.forename: Alireza
authors.initials: A
authors.lastname: Gharabaghi
mesh_terms: D000328:Adult; D000368:Aged; D001611:Beta Rhythm / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D002908:Chronic Disease; D004569:Electroencephalography / Q000379:methods; D005260:Female; D006801:Humans; D019018:Imagery, Psychotherapy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology; D020521:Stroke / Q000503:physiopathology / Q000523:psychology* / Q000628:therapy*; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D016896:Treatment Outcome
keywords: Beta oscillations; Beta power; Beta power variance; Brain-computer interface; Brain-machine interface; Rehabilitation technology; Stroke; Transcranial alternating current stimulation; Upper limb rehabilitation