Characterizing Cortical Responses Evoked by Robotic Joint Manipulation after Stroke

Cortical damage after a stroke often affects movement control, resulting in impairments such as paresis and synergies. Although some recover, most stroke survivors are left with reduced function of the upper limb, which has a severe impact on their activities of daily living. People who have suffered a stroke demonstrate heterogeneous impairments due to large variability in lesion location and extent; thus, rehabilitation should be tailored to each individual. Design and evaluation of rehabilitation programs requires a thorough understanding of the healthy and impaired sensorimotor system. Impairments to the motor system have been extensively investigated. On the contrary, the sensory aspects of impaired motor control have received less attention. This thesis intends to characterize the relation between somatosensory information from the periphery and the corresponding cortical responses using electroencephalography (EEG).Biomechatronics & Human-Machine Contro

Targeted brain activation using isometric motor tasks during functional magnetic resonance imaging

Over 0.9% of the population suffers from a movement disorder. The pathophysiology of most movement disorders remains unknown, thereby impairing effective diagnosis and consequently effective treatment. Abnormal activity of the cerebellum (CBL) and basal ganglia (BG) has been implicated in many movement disorders, including Parkinsonian tremor and dystonia. Selectively activating these brain regions may help identify pathological changes and expedite diagnosis. Dedicated pairs of isometric wrist flexion tasks with and without visual feedback of the exerted torque were devised to selectively activate the CBL and BG in healthy subjects (N=5), while ensuring safety and keeping artifacts to a minimum. Increased activity in CBL and BG (putamen) was found during a constant torque task with visual feedback compared to a constant torque task without visual feedback. Increased BG (caudate nucleus) activity was found when comparing a torque task with visual feedback where flexion and rest were rapidly alternated, to the same task without visual feedback. Increased activity in the CBL was found during a constant torque task with visual feedback with an added visual error compared to a constant torque task with normal visual feedback. This study shows that specific pairs of motor tasks using the wrist and simple MR-compatible equipment allow for targeted activation of CBL and BG and paves the way for more extensive research and eventually improved diagnosis of patients.BMBioMechanical EngineeringMechanical, Maritime and Materials Engineerin

Quantifying nonlinear contributions to cortical responses evoked by continuous wrist manipulation

Cortical responses to continuous stimuli as recorded using either magneto- or electroencephalography (EEG) have shown power at harmonics of the stimulatedfrequency, indicating nonlinear behavior. Even though the selection of analysis techniques depends on the linearity of the system under study, the importance of nonlinear contributions to cortical responses has not been formallyaddressed.The goal of this paper is to quantify the nonlinear contributions to the cortical response obtained fromcontinuous sensory stimulation. EEG was used to record the cortical response evoked by continuousmovement of the wrist joint of healthy subjects applied with a robotic manipulator. Multisine stimulus signals (i.e., the sum of several sinusoids) elicit a periodic cortical response and allowto assessthe nonlinear contributions to the response.Wrist dynamics (relation between joint angle and torque) were successfully linearized, explaining 99% of the response. In contrast, the cortical response revealed a highly nonlinear relation;where most power ( ∼ 80%) occurred at non-stimulated frequencies. Moreover, only 10% of the response could be explained using a nonparametric linear model. These results indicate that the recorded evoked cortical responsesare governed by nonlinearities and that linear methods do not suffice when describing the relation between mechanical stimulus and cortical response.Accepted Author ManuscriptBiomechatronics & Human-Machine Contro

Evaluating the Tm2+ 4f125d1 → 4f13 and 4f13 → 4f13 Luminescence and Quenching Dynamics in Orthorhombic BaCl2

The luminescence properties of Tm2+-doped BaCl2 with an orthorhombic structure have been studied as a function of temperature and compared to other Tm2+-doped chlorides. In addition to the 2F5/2 → 2F7/2 (4f13 → 4f13) line emission, two 4f125d1 → 4f13 band emissions are observed at 20 K that can be ascribed to the spin-allowed (3H6,5d1)S=1/2 → 2F7/2 and spin-forbidden (3H6,5d1)S=3/2 → 2F7/2 transitions. So far, the Tm2+ spin-allowed (3H6,5d1)S=1/2 → 2F7/2 transition has only been identified in Tm2+-doped iodides and some bromides but never before in a Tm2+-doped chloride. Its presence in orthorhombic BaCl2:Tm2+ is explained by the absence of a (3H6,5d1)S=1/2 → (3H6,5d1)S=3/2 energy transfer process. As the temperature increases, both 4f125d1 → 4f13 emissions undergo rapid quenching and are no longer observed at 120 K, resulting in an intensity increase of the 4f13 → 4f13 emission. However, above 100 K, the intensity of the 4f13 → 4f13 emission also decreases, most likely due to quenching via (3H6,5d1)S=3/2 → 2F7/2 interband crossing, as enabled by the exceptionally large 4f125d1 Stokes shift.RST/Luminescence Material