Kevin obtained a PhD in Neuroscience from Northwestern University while working in the Physical Therapy and Human Movement Sciences Department and a BS/BA in Psychology and English from Boston College. His dissertation research focused on understanding the neural mechanisms underlying upper extremity impairments in individuals with chronic stroke and subsequent motor improvements following novel interventions. His postdoctoral work at Stanford with Dr. Helen Bronte-Stewart focuses on the neural features associated with gait impairment in individuals with Parkinson's disease using a combination of structural imaging, neurophysiology, and kinematic analysis. He was awarded a Postdoctoral Fellowship for Basic Scientists from the Parkinson's Foundation to investigate the cognitive correlates of gait impairment in Parkinson's disease.
Bachelor of Arts, Boston College, English (2014)
Doctor of Philosophy, Northwestern University, Neuroscience (2019)
Bachelor of Science, Boston College, Psychology (2014)
Helen Bronte-Stewart, Postdoctoral Faculty Sponsor
Limited capacity for ipsilateral secondary motor areas to support hand function post-stroke
JOURNAL OF PHYSIOLOGY-LONDON
2020; 598 (11): 2153–67
Ipsilateral-projecting corticobulbar pathways, originating primarily from secondary motor areas, innervate the proximal and even distal portions, although they branch more extensively at the spinal cord. It is currently unclear to what extent these ipsilateral secondary motor areas and subsequent cortical projections may contribute to hand function following stroke-induced damage to one hemisphere. In the present study, we provide both structural and functional evidence indicating that individuals increasingly rely on ipsilateral secondary motor areas, although at the detriment of hand function. Increased activity in ipsilateral secondary motor areas was associated with increased involuntary coupling between shoulder abduction and finger flexion, most probably as a result of the low resolution of these pathways, making it increasingly difficult to open the hand. These findings suggest that, although ipsilateral secondary motor areas may support proximal movements, they do not have the capacity to support distal hand function, particularly for hand opening.Recent findings have shown connections of ipsilateral cortico-reticulospinal tract (CRST), predominantly originating from secondary motor areas to not only proximal, but also distal muscles of the arm. Following a unilateral stroke, CRST from the ipsilateral side remains intact and thus has been proposed as a possible backup system for post-stroke rehabilitation even for the hand. We argue that, although CRST from ipsilateral secondary motor areas can provide control for proximal joints, it is insufficient to control either hand or coordinated shoulder and hand movements as a result of its extensive spinal branching compared to contralateral corticospinal tract. To address this issue, we combined magnetic resonance imaging, high-density EEG, and robotics in 17 individuals with severe chronic hemiparetic stroke and 12 age-matched controls. We tested for changes in structural morphometry of the sensorimotor cortex and found that individuals with stroke demonstrated higher grey matter density in secondary motor areas ipsilateral to the paretic arm compared to controls. We then measured cortical activity when participants were attempting to generate hand opening either supported on a table or when lifting against a shoulder abduction load. The addition of shoulder abduction during hand opening increased reliance on ipsilateral secondary motor areas in stroke, but not controls. Crucially, the increased use of ipsilateral secondary motor areas was associated with decreased hand opening ability when lifting the arm as a result of involuntary coupling between the shoulder and wrist/finger flexors. Taken together, this evidence implicates a compensatory role for ipsilateral (i.e. contralesional) secondary motor areas post-stroke, although with no apparent capacity to support hand function.
View details for DOI 10.1113/JP279377
View details for Web of Science ID 000528549500001
View details for PubMedID 32144937
View details for PubMedCentralID PMC7266727
Coordination of multiple joints increases bilateral connectivity with ipsilateral sensorimotor cortices
2020; 207: 116344
Although most activities of daily life require simultaneous coordination of both proximal and distal joints, motor preparation during such movements has not been well studied. Previous results for motor preparation have focused on hand/finger movements. For simple hand/finger movements, results have found that such movements typically evoke activity primarily in the contralateral motor cortices. However, increasing the complexity of the finger movements, such as during a distal sequential finger-pressing task, leads to additional recruitment of ipsilateral resources. It has been suggested that this involvement of the ipsilateral hemisphere is critical for temporal coordination of distal joints. The goal of the current study was to examine whether increasing simultaneous coordination of multiple joints (both proximal and distal) leads to a similar increase in coupling with ipsilateral sensorimotor cortices during motor preparation compared to a simple distal movement such as hand opening. To test this possibility, 12 healthy individuals participated in a high-density EEG experiment in which they performed either hand opening or simultaneous hand opening while lifting at the shoulder on a robotic device. We quantified within- and cross-frequency cortical coupling across the sensorimotor cortex for the two tasks using dynamic causal modeling. Both hand opening and simultaneous hand opening while lifting at the shoulder elicited coupling from secondary motor areas to primary motor cortex within the contralateral hemisphere exclusively in the beta band, as well as from ipsilateral primary motor cortex. However, increasing the task complexity by combining hand opening while lifting at the shoulder also led to an increase in cross-frequency coupling within the ipsilateral hemisphere including theta, beta, and gamma frequencies, as well as a change in the coupling frequency of the interhemispheric coupling between the primary motor and premotor cortices. These findings demonstrate that increasing the demand of joint coordination between proximal and distal joints leads to increases in communication with the ipsilateral hemisphere as previously observed in distal sequential finger tasks.
View details for DOI 10.1016/j.neuroimage.2019.116344
View details for Web of Science ID 000509662600011
View details for PubMedID 31730924
View details for PubMedCentralID PMC7192312
- Neural Closed loop deep brain stimulation for freezing of Gait. Brain stimulation 2020
Intervention-induced changes in neural connectivity during motor preparation may affect cortical activity at motor execution.
2020; 10 (1): 7326
Effective interventions have demonstrated the ability to improve motor function by reengaging ipsilesional resources, which appears to be critical and feasible for hand function recovery even in individuals with severe chronic stroke. However, previous studies focus on changes in brain activity related to motor execution. How changes in motor preparation may facilitate these changes at motor execution is still unclear. To address this question, 8 individuals with severe chronic hemiparetic stroke participated in a device-assisted intervention for seven weeks. We then quantified changes in both coupling between regions during motor preparation and changes in topographical cortical activity at motor execution for both hand opening in isolation and together with the shoulder using high-density EEG. We hypothesized that intervention-induced changes in cortico-cortico interactions during motor preparation would lead to changes in activity at motor execution specifically towards an increased reliance on the ipsilesional hemisphere. In agreement with this hypothesis, we found that, following the intervention, individuals displayed a reduction in coupling from ipsilesional M1 to contralesional M1 within gamma frequencies during motor preparation for hand opening. This was followed by a reduction in activity in the contralesional primary sensorimotor cortex during motor execution. Similarly, during lifting and opening, a shift to negative coupling within ipsilesional M1 from gamma to beta frequencies was accompanied by an increase in ipsilesional primary sensorimotor cortex activity following the intervention. Together, these results show that intervention-induced changes in coupling within or between motor regions during motor preparation may affect cortical activity at execution.
View details for DOI 10.1038/s41598-020-64179-x
View details for PubMedID 32355238
View details for PubMedCentralID PMC7193567
Improving Hand Function of Severely Impaired Chronic Hemiparetic Stroke Individuals Using Task-Specific Training With the Reln-Hand System: A Case Series
FRONTIERS IN NEUROLOGY
2018; 9: 923
Purpose: In this study, we explored whether improved hand function is possible in poststroke chronic hemiparetic individuals with severe upper limb motor impairments when they participate in device-aided task-specific practice. Subjects: Eight participants suffering from chronic stroke (>1-year poststroke, mean: 11.2 years) with severely impaired upper extremity movement (Upper Extremity Subscale of the Fugl-Meyer Motor Assessment (UEFMA) score between 10 and 24) participated in this study. Methods: Subjects were recruited to participate in a 20-session intervention (3 sessions/7 weeks). During each session, participants performed 20-30 trials of reaching, grasping, retrieving, and releasing a jar with the assistance of a novel electromyography-driven functional electrical stimulation (EMG-FES) system. This EMG-FES system allows for Reliable and Intuitive use of the Hand (called ReIn-Hand device) during multi-joint arm movements. Pre-, post-, and 3-month follow-up outcome assessments included the UEFMA, Cherokee McMaster Stroke Assessment, grip dynamometry, Box and Blocks Test (BBT), goniometric assessment of active and passive ranges of motion (ROMs) of the wrist and the metacarpophalangeal flexion and extension (II, V fingers), Nottingham Sensory Assessment-Stereognosis portion (NSA), and Cutaneous Sensory Touch Threshold Assessment. Results: A nonparametric Friedman test of differences found significant changes in the BBT scores (χ2 = 10.38, p < 0.05), the passive and active ROMs (χ2 = 11.31, p < 0.05 and χ2 = 12.45, p < 0.01, respectively), and the NSA scores (χ2 = 6.42, p < 0.05) following a multi-session intervention using the ReIn-Hand device. Conclusions: These results suggest that using the ReIn-Hand device during reaching and grasping activities may contribute to improvements in gross motor function and sensation (stereognosis) in individuals with chronic severe UE motor impairment following stroke.
View details for DOI 10.3389/fneur.2018.00923
View details for Web of Science ID 000449422000001
View details for PubMedID 30464754
View details for PubMedCentralID PMC6234834
Nucleus accumbens mu opioid receptors regulate context-specific social preferences in the juvenile rat
2018; 89: 59–68
The μ opioid receptor (MOR) in the nucleus accumbens (NAc) is involved in assigning pleasurable, or hedonic value to rewarding stimuli. Importantly, the hedonic value of a given rewarding stimulus likely depends on an individual's current motivational state. Here, we examined the involvement of MORs in the motivation to interact with a novel or a familiar (cage mate) conspecific in juvenile rats. First, we demonstrated that the selective MOR antagonist CTAP administered into the NAc reduces social novelty preference of juvenile males, by decreasing the interaction time with the novel conspecific and increasing the interaction time with the cage mate. Next, we found that a 3-h separation period from the cage mate reduces social novelty preference in both juvenile males and females, which was primarily driven by an increase in interaction time with the cage mate. Last, we showed that MOR agonism (intracerebroventricularly or in the NAc) restored social novelty preference in juvenile males that did not show social novelty preference following social isolation. Taken together, these data support a model in which endogenous MOR activation in the NAc facilitates the relative hedonic value of novel over familiar social stimuli. Our results may implicate the MOR in neuropsychiatric disorders characterized by altered social motivation, such as major depression and autism spectrum disorder.
View details for DOI 10.1016/j.psyneuen.2017.12.017
View details for Web of Science ID 000430625700009
View details for PubMedID 29331800
Neural Plasticity in Moderate to Severe Chronic Stroke Following a Device-Assisted Task-Specific Arm/Hand Intervention
FRONTIERS IN NEUROLOGY
2017; 8: 284
Currently, hand rehabilitation following stroke tends to focus on mildly impaired individuals, partially due to the inability for severely impaired subjects to sufficiently use the paretic hand. Device-assisted interventions offer a means to include this more severe population and show promising behavioral results. However, the ability for this population to demonstrate neural plasticity, a crucial factor in functional recovery following effective post-stroke interventions, remains unclear. This study aimed to investigate neural changes related to hand function induced by a device-assisted task-specific intervention in individuals with moderate to severe chronic stroke (upper extremity Fugl-Meyer < 30). We examined functional cortical reorganization related to paretic hand opening and gray matter (GM) structural changes using a multimodal imaging approach. Individuals demonstrated a shift in cortical activity related to hand opening from the contralesional to the ipsilesional hemisphere following the intervention. This was driven by decreased activity in contralesional primary sensorimotor cortex and increased activity in ipsilesional secondary motor cortex. Additionally, subjects displayed increased GM density in ipsilesional primary sensorimotor cortex and decreased GM density in contralesional primary sensorimotor cortex. These findings suggest that despite moderate to severe chronic impairments, post-stroke participants maintain ability to show cortical reorganization and GM structural changes following a device-assisted task-specific arm/hand intervention. These changes are similar as those reported in post-stroke individuals with mild impairment, suggesting that residual neural plasticity in more severely impaired individuals may have the potential to support improved hand function.
View details for DOI 10.3389/fneur.2017.00284
View details for Web of Science ID 000403390400001
View details for PubMedID 28659863
View details for PubMedCentralID PMC5469871