Chronic stroke is often accompanied by tactile impairments that contribute to long-term disability in activities of daily living. While new rehabilitative interventions recently became available in the motor domain by using transcranial direct current stimulation (tDCS), there is no generally accepted treatment for tactile impairments after chronic stroke. Previous studies in healthy volunteers demonstrated that tactile acuity and haptic skills can be improved by applying a passive learning protocol to the fingertip (peripheral high-frequency stimulation, pHFS). Based on these findings, the purpose of this protocol is to enhance the beneficial effect of pHFS on implicit tactile and haptic learning in chronic stroke patients by a combined application of pHFS with tDCS (pHFS+tDCS) applied to the somatosensory cortex of the affected hemisphere. This approach might identify novel strategies to enhance functional recovery after stroke and might provide deeper insight into mechanistic information on the neural substrates involved in these behavioral gains. Primary outcome measures will be performance in a tactile grating orientation discrimination task (GOT) and in a haptic object recognition task. In order to obtain descriptive preliminary information on the relation between sensory improvements and motor deficits in chronic stroke patients, secondary outcome measures will be fine motor tasks such as a tapping task and a pegboard test (PBT) that require manual dexterity, handeye coordination, steadiness, and perceptual motor skills. To identify the operating mechanisms underlying hypothesized performance improvements after pHFS+tDCS, we will use paired-pulse protocols to evaluate changes in cortical excitability as well as fMRI in a subset of patients to identify cortical map reorganization in primary (SI) and secondary (SII) somatosensory cortex as well as in primary motor cortex (MI). Healthy volunteers will be tested (a) since there are no data available on performance of the haptic task in healthy subjects, (b) to obtain descriptive information on the influence of our interventions on this task for hypothesis generation purposes in our future investigations, and (c) because sensorimotor performance in the non-paretic hand of stroke patients is often not normal and therefore a poor sole control for performance of the paretic hand. Studies in chronic stroke patients will help address the main experimental hypothesis.
- INCLUSION CRITERIA: We will include left- and right-handed stroke patients, aged 18-90 years, with thromboembolic or hemorrhagic hemispheric lesions at least 3 months after the stroke. We will choose patients who initially had a severe motor paresis (below MRC grade 2), and subsequently recovered to the point that they have a residual motor deficit but can perform the required tasks. Moreover, only chronic stroke patients with moderate tactile deficits (defined by absolute touch thresholds below 4 N using von Frey filaments) who are able to differentiate the alignment of a grating dome (either orthogonal or parallel to the index finger) of at least 5 mm grooves that is applied on the fingertip will be included in the protocol. Assessment of the initial functional state will be taken either from patient reports or medical records. Right-handed healthy volunteers, aged 18-90 years, should be able to concentrate on the required tasks. Handedness will be assessed by the Edinburgh inventory scale as well as the hand dominance test (HDT). We will additionally perform a pregnancy test for women of child-bearing potential. All experimental sessions will be on outpatient basis. EXCLUSION CRITERIA: Chronic stroke patients will be not be eligible for the study if they: - are unable to perform the behavioral tasks, - have a sensory neglect, - have had more than one clinical stroke, - have both sides of the brain affected, - have had a stroke in the cerebellum or brainstem, - have a history of alcohol or drug abuse or severe language disturbances or serious cognitive deficits, - have uncontrolled medical problems, such as heart, lung or kidney disease, epilepsy or diabetes mellitus, - have severe tactile deficits (defined by Frey filaments exerting a force of 4 N to the distal pad of the finger on the paretic and non-paretic hand), - are pregnant, - have a cardiac pacemaker, intracardiac lines, implanted medication pumps, neural stimulators, metal in the cranium, with the exception of dental braces in the mouth. Exclusion criteria for healthy volunteers: Healthy volunteers will not be eligible for the study if they: - are unable to perform the tasks, - have a history of alcohol or drug abuse or severe language disturbances or serious cognitive deficits, - have uncontrolled medical problems, such as heart, lung or kidney disease, epilepsy or diabetes mellitus, - have severe tactile deficits (defined by Frey filaments exerting a force of 4 N to the distal pad of the finger), - are pregnant, - have a cardiac pacemaker, intracardiac lines, implanted medication pumps, neural stimulators, metal in the cranium except in the mouth, dental braces.