Inclusion criteria for aged matched healthy group  Male or female whose age range between 40 and 75 no known neurological injuries  Exclusion criteria for aged matched healthy group  have an orthopedic disorder involving upper limbs; have a history of any neurologic disease; have any history of epilepsy of the potential participants and/or their family members; had an adverse reaction to TMS; are unable to consent; are pregnant.  Inclusion criteria for stroke group  male or female hemiparetic chronic stroke survivors; age ranging between 40-75 year; with single unilateral ischemic or hemorrhagic middle cerebral artery stroke; neurologically stable for >6 months; have an expectation that current medication will be maintained without changes for at least 3 months. Stable use of anti-spasticity medication (e.g., baclofen, diazepam, tizanidine) is accepted; with moderate-to-severe impairments (FMA<45/66); with weak wrist extension (i.e., <4 by manual muscle strength test); eligible to receive transcranial magnetic stimulation (TMS), and extensor carpi radialis (ECR) motor evoked potential (MEP) must be present in the more affected arm; without severe spasticity (Modified Ashworth (MA) <4); have not received botulinum toxin on the impaired arm within 3 months.  Exclusion criteria for stroke group  have an orthopedic disorder involving upper limbs; have no measurable MEP elicited in the ECR; unable to produce any voluntary ECR EMG activity; cognitive impairment sufficient to interfere with informed consent or successful completion of the protocol (Montreal Cognitive Assessment (MoCA) score < 26); a history of another neurologic disease; a history of vertigo; a history of vestibular or cochlear dysfunction; have a history of convulsion or a seizure; anesthesia of joint position sense in upper limbs; are pregnant or have a chance that they might be (self-reported); have metal in the brain/skull (except titanium; e.g. splinters, fragments, clips, etc.); have cochlear implants; have an implanted neurostimulator (DBS, epidural/subdural, VNS); have a cardiac pacemaker or intracardiac lines or metal in the body; have a medication infusion device; are taking any medications to treat mental illness; have spinal or ventricular derivations; had an adverse reaction to TMS.