Michael J. Cohen’s research while affiliated with California State University, Long Beach and other places

Learning to perform a skilled behavior is affected by the context of the practice session and the frequency of augmented feedback. We studied the combined effect of these variables in the acquisition of a ballistic, bi-directional lever movement pattern involving four different target locations as measured by performance in practice, retention, and transfer tests. Augmented feedback was presented in either an every-trial or a faded schedule during random and blocked practice. Consistent with the contextual interference effect, the blocked practice group produced lower errors in acquisition, but the random practice group outperformed the blocked practice group in both retention and transfer. In contrast, faded feedback did not have a beneficial effect on learning and degraded learning when provided during blocked practice. While the results were consistent with previous findings of random and blocked practice, they were not consistent with previous findings of reduced feedback frequencies.

Cerebral control of foot movements has received limited study. Functional MRI compared slow with rapid foot movement, and right (dominant) with left foot movement. Brain activation during right, as compared with left, foot movement was larger, with higher amplitude task-related motor cortex signal change, and higher laterality index. Brain activation during fast, as compared with slow, foot movement was larger in cortical and cerebellar areas but smaller in deep gray areas. Some principles of cerebral control of hand movement extend to foot, but exceptions found include that dominant foot movement showed greater activation than did nondominant, and faster foot movements activated bilateral deep gray matter structures less than did slower. Results might have utility in trials of restorative therapies.

Evidence suggests that executed, imagined, and observed movements share neural substrates, however, brain activation during the performance of these three tasks has not yet been examined during lower extremity movements. Functional MRI was performed in 10 healthy right-footed participants during imagined, executed, and observed right ankle movements. Task compliance was high, confirmed via behavioral assessment and electromyographic measurements. Each task was also associated with its own profile of regional activation, however, overall, regional activation showed substantial overlap across the three lower extremity motor tasks. The findings suggest the utility of continued efforts to develop motor imagery and observation programs for improving lower extremity function in a range of clinical settings.

Abnormalities in brain motor system function are present following spinal cord injury (SCI) and could reduce effectiveness of restorative interventions. Motor imagery training, which can improve motor behavior and modulate brain function, might address this concern but has not been examined in subjects with SCI. Ten subjects with SCI and complete tetra-/paraplegia plus ten healthy controls underwent assessment before and after 7 days of motor imagery training to tongue and to foot. Motor imagery training significantly improved the behavioral outcome measure, speed of movement, in non-paralyzed muscles. Training was also associated with increased fMRI activation in left putamen, an area associated with motor learning, during attempted right foot movement in both groups, despite foot movements being present in controls and absent in subjects with SCI. This fMRI change was absent in a second healthy control group serially imaged without training. In subjects with SCI, training exaggerated, rather than normalized, baseline derangement of left globus pallidus activation. The current study found that motor imagery training improves motor performance and alters brain function in subjects with complete SCI despite lack of voluntary motor control and peripheral feedback. These effects of motor imagery training on brain function have not been previously described in a neurologically impaired population, and were similar to those found in healthy controls. Motor imagery might be of value as one component of a restorative intervention.

Most therapies under development to restore motor function after spinal cord injury (SCI) assume intact brain motor functions. To examine this assumption, 12 patients with chronic, complete SCI and 12 controls underwent functional MRI during attempted, and during imagined, right foot movement, each at two force levels. In patients with SCI, many features of normal motor system function were preserved, however, several departures from normal were apparent: (i) volume of activation was generally much reduced, e.g. 4-8% of normal in primary sensorimotor cortex, in the setting of twice normal variance in signal change; (ii) abnormal activation patterns were present, e.g. increased pallido-thalamocortical loop activity during attempted movement and abnormal processing in primary sensorimotor cortex during imagined movement; and (iii) modulation of function with change in task or in force level did not conform to patterns seen in controls, e.g. in controls, attempted movement activated more than imagined movement did within left primary sensorimotor cortex and right dorsal cerebellum, while imagined movement activated more than attempted movement did in dorsolateral prefrontal cortex and right precentral gyrus. These modulations were absent in patients with SCI. Many features of brain motor system function during foot movement persist after chronic complete SCI. However, substantial derangements of brain activation, poor modulation of function with change in task demands and emergence of pathological brain events were present in patients. Because brain function is central to voluntary movement, interventions that aim to improve motor function after chronic SCI likely also need to attend to these abnormalities of brain function.

This experiment used functional magnetic resonance imaging (fMRI) to compare functional neuroanatomy associated with executed and imagined hand movements in novel and skilled learning phases. We hypothesized that 1 week of intensive physical practice would strengthen the motor representation of a hand motor sequence and increase the similarity of functional neuroanatomy associated with executed and imagined hand movements. During fMRI scanning, a right-hand self-paced button press sequence was executed and imagined before (NOVEL) and after (SKILLED) 1 week of intensive physical practice (n = 54; right-hand dominant). The mean execution rate was significantly faster in the SKILLED (3.8 Hz) than the NOVEL condition (2.5 Hz) (P < 0.001), but there was no difference in execution errors. Activation foci associated with execution and imagery was congruent in both the NOVEL and SKILLED conditions, though activation features were more similar in the SKILLED versus NOVEL phase. In the NOVEL phase, activations were more extensive during execution than imagery in primary and secondary cortical motor volumes and the cerebellum, while during imagery activations were greater in the striatum. In the SKILLED phase, activation features within these same volumes became increasingly similar for execution and imagery, though imagery more heavily activated premotor areas, inferior parietal lobe, and medial temporal lobe, while execution more heavily activated the precentral/postcentral gyri, striatum, and cerebellum. This experiment demonstrated congruent activation of the cortical and subcortical motor system during both novel and skilled learning phases, supporting the effectiveness of motor imagery-based mental practice techniques for both the acquisition of new skills and the rehearsal of skilled movements.

Motor behavior and sensorimotor activation of the cerebrum and cerebellum were measured before and after motor imagery-based mental practice (MP) and physical practice (PP) of a sequential motor task. Two-button-press sequences (A, B) were performed outside a magnetic resonance imaging scanner and at 2 Hz inside the scanner during a pretest. Participants (n = 39) completed PP, MP, or no practice (NP) of Sequence A for 1 week and were posttested. Sequence A performance improved 121%, 86%, and 4% for the PP, MP, and NP groups, respectively (p < 0.05), while Sequence B improved 56%, 40%, and 38% (p > 0.05). PP improvements were accompanied by increased striatal and decreased cerebellar activation, while MP improvements were accompanied by increased cerebellar, premotor, and striatal activation. The efficacy of MP for activating cerebral and cerebellar sensorimotor networks suggests that MP might be an effective substitute or complement to PP to activate compensatory networks for motor rehabilitation.

Cortical reorganization can occur after deaf-ferentation due to loss of a limb, but the nature of the cortical reorganization after spinal cord injury (SCI) is still in debate. Using a 1.5T MRI, we scanned paraplegic and noninjured participants during hand movement and palm stimulation, to determine whether longterm paraplegics would show different patterns of cortical activity from the noninjured participants. The SCI group showed stronger activation in areas posterior, rather than superior, to the areas activated by non-SCIs. Conversely, the non-SCIs showed stronger activation in more anterior areas. The signal at each individual's maximally significant voxel had a greater modulation for the SCI group than for the non-SCIs, in response to movement. In this study of sensory and motor representations within the same subjects, the authors show for the first time the increase in the BOLD fMRI signal modulation in SCI. The authors do not find evidence of expansion of the hand representation into nearby cortical areas, and they corroborate previous EEG studies indicating a posterior shift for hand motor representation after SCI, while showing that the sensory representation does not undergo a posterior shift of similar magnitude. The difference between the reorganization found here and the reorganization typically found following amputations suggests a rationale for the differences in neuropathic pain symptoms following a spinal cord injury or amputation.

Certain brain-computer interface (BCI) methods use intrinsic signals from the motor cortex to control neuroprosthetic devices. The organization of the motor pathways in those populations likely to use neuroprosthetic devices, therefore, needs to be determined; there is evidence that following disease or injury the representation of the body in the motor cortex may change. In this study, functional MRI measures of somatotopy following spinal cord injury (SCI) showed evidence of changes in limb representations in the motor cortex. Subjects with chronic SCI had unusual cortical patterns of activity when attempting to move limbs below their injury; amputees showed a more normal somatotopy. The functional reorganization may affect optimal implanted electrode placements for invasive BCI methods for these different populations.