Donald J. Crammond

Differential relation of discharge in primary motor cortex and premotor cortex to movements versus actively maintained postures during a reaching task

The activity of cells in primary motor cortex (MI) and dorsal premotor cortex (PMd) were compared during reaching movements in a reaction-time (RT) task, without prior instructions, which required precise control of limb posture before and after movement. MI neurons typically showed strong, directionally tuned activity prior to and during movement as well as large gradations of tonic activity while holding the limb over different targets. The directionality of their movementand posture-related activity was generally similar. Proximal-arm muscles behaved similarly. This is consistent with a role for MI in the moment-to-moment control of motor output, including both movement and actively maintained postures, and suggests a common functional relation for MI cells to both aspects of motor behavior. In contrast, PMd cells were generally more phasic, frequently emitting only strong bursts of activity confined mainly to the behavioral reaction time before movement onset. PMd tonic activity during different postures was generally weaker than in MI, and showed a much more variable relation with their movement-related directional tuning. These results imply that the major contribution of PMd to this RT task occurred prior to the onset of movement itself, consistent with a role for PMd in the selection and planning of visually guided movements. Furthermore, the nature of the relative contribution of PMd to movement versus actively maintained postures appears to be fundamentally different from that in MI. Finally, there was a continuous gradient of changes in responses across the rostrocaudal extent of the precentral gyrus, with no abrupt transition in response properties between PMd and MI.

Neuronal activity in primate parietal cortex area 5 varies with intended movement direction during an instructed-delay period

SummaryA monkey was trained to make arm movements to visual targets immediately after presentation of a GO signal, either in a visual reaction-time paradigm (CONTROL task), or after an instructed-delay period of variable duration, during which a CUE stimulus signalled the direction of the impending movement (DELAY task). The activity of 98 area 5 cells recorded in 2 hemispheres varied with movement direction in the CONTROL task. This included 60 “early” cells which showed directional activity changes prior to movement onset. In the DELAY task, 54/98 cells (55%) showed activity changes during the instructed-delay period which varied with the direction of the impending movement. Most of these (45/54, 83%) were “early” cells. Forty proximal arm-related cells were recorded in adjacent area 2. In contrast to area 5, only 2/40 area 2 cells showed any evidence of changes in activity varying with intended movement direction during the instructed-delay period. The origin of area 5 activity changes during an instructed-delay period which are related to intended direction of a delayed movement is uncertain, but its presence is consistent with a number of proposed roles for area 5.

Neuronal correlates in posterior parietal lobe of the expectation of events

During studies of response properties of single units in the posterior parietal cortex of 6 awake monkeys, 168 neurons were encountered (7.1% of examined units) which showed anticipatory types of activity. These neurons were found on either side of the intraparietal sulcus. In area 5, this expectation activity was expressed as a change in discharge rate whenever a specific body part (e.g. hand or shoulder) was approached by the investigator as though contact would be made. Invariably the neurons also responded to cutaneous and/or proprioceptive stimulation of the target body area. In area 7a the same type of response was also found but not always with a corresponding somatosensory receptive field. In addition, many neurons increased discharge rates (or rarely, decreased them) immediately prior to the expected occurrence of a reward, a visual task cue, or on hearing the approaching footsteps of a familiar person. None of these responses were correlated to eye movements, nor could they be attributed to any other body movement.

Human motor cortical activity recorded with Micro-ECoG electrodes, during individual finger movements

In this study human motor cortical activity was recorded with a customized micro-ECoG grid during individual finger movements. The quality of the recorded neural signals was characterized in the frequency domain from three different perspectives: (1) coherence between neural signals recorded from different electrodes, (2) modulation of neural signals by finger movement, and (3) accuracy of finger movement decoding. It was found that, for the high frequency band (60–120 Hz), coherence between neighboring micro-ECoG electrodes was 0.3. In addition, the high frequency band showed significant modulation by finger movement both temporally and spatially, and a classification accuracy of 73% (chance level: 20%) was achieved for individual finger movement using neural signals recorded from the micro-ECoG grid. These results suggest that the micro-ECoG grid presented here offers sufficient spatial and temporal resolution for the development of minimally-invasive brain-computer interface applications.

Measurements of human forearm viscoelasticity

In human subjects, stiffness of the relaxed elbow was measured by three methods, using a forearm manipulandum coupled to a.d.c. torque motor. Elbow stiffness calculated from frequency response characteristics increased as the driving amplitude decreased. Step displacements of the forearm produced restoring torques linearly related to the displacement. The stiffness was very similar to that calculated from natural frequencies at amplitudes above 0.1 rad. Thirdly, elbow stiffness was estimated from brief test pulses, 120 ms in duration, by mathematically simulating the torque-displacement functions. Stiffness values in the limited linear range (under +/- 0.1 rad) were higher than in the linear range of the first two methods. A major component of elbow stiffness appears to decay within 1 s. The coefficients of viscosity determined from the simulation were, however, very similar to those calculated from the frequency response. Test pulse simulation was then used to determine joint impedance for different, actively maintained elbow angles. Joint stiffness and viscosity increased with progressive elbow flexion.

Intraoperative somatosensory evoked potential monitoring during cervical spine corpectomy surgery: experience with 508 cases.

Study Design. Retrospective review. Objectives. To review consecutive cases of cervical spine corpectomy surgery performed with intraoperative somatosensory-evoked potential (SSEP) monitoring. Summary of Background Data. There is controversy about the utility of SSEP monitoring during anterior cervical spine surgery. There is no study in the literature that has specifically evaluated the utility of SSEP monitoring for cervical spine corpectomy surgery. Methods. Intraoperative SSEP tracings for 508 patients (average age, 55.7 years; 268 male, 240 female) who underwent anterior cervical fusion with single-level or multilevel corpectomies were reviewed. Intraoperative and postoperative records were analyzed to determine if any new neurologic deficits developed when the patients woke up from anesthesia. Results. The overall incidence of a new postoperative neurologic deficit in this series of patients was 2.4% (11 with nerve root injury, 1 with quadriplegia). The incidence of significant SSEP changes was 5.3% (27 of 508 patients). The most common identifiable cause of SSEP changes was hypotension, and the most common neurologic deficit was deltoid (C5) weakness. One patient had irreversible SSEP changes, and he woke up with new-onset quadriplegia. The calculated sensitivity and specificity of intraoperative SSEP monitoring for detecting impending or resultant intraoperative iatrogenic neurologic injury were 77.1% and 100%, respectively. However, if the isolated nerve root injuries are removed from the analysis, then both the calculated sensitivity and the negative predictive values were 100%. Conclusions. Intraoperative SSEP monitoring can alert the surgeon to adverse iatrogenic intraoperative events with potential for neurologic injury. Most SSEP signal changes are reversible and do not result in a clinical deficit. Isolated nerve root injury appears to be the most common iatrogenic intraoperative injury during cervical spine corpectomy surgery.

Microvascular Decompression for Hemifacial Spasm: Evaluating Outcome Prognosticators Including the Value of Intraoperative Lateral Spread Response Monitoring and Clinical Characteristics in 293 Patients

Hemifacial spasm is a socially disabling condition that manifests as intermittent involuntary twitching of the eyelid and progresses to muscle contractions of the entire hemiface. Patients receiving microvascular decompression of the facial nerve demonstrate an abnormal lateral spread response (LSR) in peripheral branches during facial electromyography. The authors retrospectively evaluate the prognostic value of preoperative clinical characteristics and the efficacy of intraoperative monitoring in predicting short- and long-term relief after microvascular decompression for hemifacial spasm. Microvascular decompression was performed in 293 patients with hemifacial spasm, and LSR was recorded during intraoperative facial electromyography monitoring. In 259 (87.7%) of the 293 patients, the LSR was attainable. Patient outcome was evaluated on the basis of whether the LSR disappeared or persisted after decompression. The mean follow-up period was 54.5 months (range, 9–102 months). A total of 88.0% of patients experienced immediate postoperative relief of spasm; 90.8% had relief at discharge, and 92.3% had relief at follow-up. Preoperative facial weakness and platysmal spasm correlated with persistent postoperative spasm, with similar trends at follow-up. In 207 patients, the LSR disappeared intraoperatively after decompression (group I), and in the remaining 52 patients, the LSR persisted intraoperatively despite decompression (group II). There was a significant difference in spasm relief between both groups within 24 hours of surgery (94.7% vs. 67.3%) (P < 0.0001) and at discharge (94.2% vs. 76.9%) (P = 0.001), but not at follow-up (93.3% vs. 94.4%) (P = 1.000). Multivariate logistic regression analysis demonstrated independent predictability of residual LSR for present spasm within 24 hours of surgery and at discharge but not at follow-up. Facial electromyography monitoring of the LSR during microvascular decompression is an effective tool in ensuring a complete decompression with long-lasting effects. Although LSR results predict short-term outcomes, long-term outcomes are not as reliant on LSR activity.

Diagnostic Value of Somatosensory Evoked Potential Changes During Carotid Endarterectomy: A Systematic Review and Meta-analysis

IMPORTANCE Perioperative stroke is a persistent complication of carotid endarterectomy (CEA) for patients with symptomatic carotid stenosis (CS). OBJECTIVE To evaluate whether changes in somatosensory evoked potential (SSEP) during CEA are diagnostic of perioperative stroke in patients with symptomatic CS. DESIGN, SETTING, AND PARTICIPANTS We searched PubMed and the World Science Database for reference lists of retrieved studies and/or experiments on SSEP use in postoperative outcomes following CEA in patients with symptomatic CS from January 1, 1950, through January 1, 2013. We independently screened all titles and abstracts to identify studies that met the inclusion criteria and extracted relevant articles in a uniform manner. Inclusion criteria included randomized clinical trials, prospective studies, or retrospective cohort reviews; population of symptomatic CS; use of intraoperative SSEP monitoring during CEA; immediate postoperative assessment and/or as long as a 3-month follow-up; a total sample size of 50 or more patients; studies with adult humans 18 years or older; and studies published in English. MAIN OUTCOME AND MEASURE Whether intraoperative SSEP changes were diagnostic of perioperative stroke indicated by postoperative neurological examination. RESULTS Four-hundred sixty-four articles were retrieved, and 15 prospective and retrospective cohort studies were included in the data analysis. A 4557-patient cohort composed the total sample population for all the studies, 3899 of whom had symptomatic CS. A change in SSEP exhibited a strong pooled mean specificity of 91% (95% CI, 86-94) but a weaker pooled mean sensitivity of 58% (95% CI, 49-68). A pooled diagnostic odds ratio for individual studies of patients with neurological deficit with changes in SSEPs was 14.39 (95% CI, 8.34-24.82), indicating that the odds of observing an SSEP change among those with neurologic deficits were 14 times higher than in individuals without neurologic deficit. CONCLUSIONS AND RELEVANCE Intraoperative SSEP is a highly specific test in predicting neurological outcome following CEA. Patients with perioperative neurological deficits are 14 times more likely to have had changes in SSEPs during the procedure. The use of SSEPs to design prevention strategies is valuable in reducing perioperative cerebral infarctions during CEA.

Somatosensory-evoked potential monitoring during instrumented scoliosis corrective procedures: validity revisited

BACKGROUND Intraoperative monitoring (IOM) using somatosensory-evoked potentials (SSEPs) plays an important role in reducing iatrogenic neurologic deficits during corrective pediatric idiopathic procedures for scoliosis. However, for unknown reasons, recent reports have cited that the sensitivity of SSEPs to detect neurologic deficits has decreased, in some to be less than 50%. This current trend, which is coincident with the addition of transcranial motor-evoked potentials, is surprising given that SSEPs are robust, reproducible responses that were previously shown to have sensitivity and specificity of >90%. PURPOSE Our primary aim was to assess whether SSEPs alone can detect impending neurologic deficits with similar sensitivity and specificity as originally reported. Our secondary aim was to estimate the potential predictive value of adding transcranial motor-evoked potentials to SSEP monitoring in idiopathic scoliosis procedures. DESIGN This was a retrospective review to analyze the efficacy of SSEP monitoring in the group of pediatric instrumented scoliosis fusion cases. PATIENT SAMPLE We retrospectively reviewed all consecutive cases of patients who underwent idiopathic scoliosis surgery between 1999 and 2009 at Childrens Hospital of Pittsburgh. We identified 477 patients who had the surgery with SSEP monitoring alone. Exclusion criteria included any patients with neuromuscular disorders or unreliable SSEP monitoring. Patients who had incomplete neurophysiology data or incomplete postoperative records were also excluded. OUTCOME MEASURES Major outcomes measured were clinically significant postoperative sensory or motor deficits, as well as significant intraoperative SSEP changes. METHODS Continuous interleaved upper- and lower-extremity SSEPs were obtained throughout the duration of all procedures. We considered a persistent 50% reduction in primary somatosensory cortical amplitude or a prolongation of response latency by >10% from baseline to be significant. Persistent changes represent significant deviation in SSEP amplitude or latency in more than two consecutive averaged trials. Patients were classified into one of four categories with respect to SSEP monitoring: true positive, false positive, true negative, and false negative. The sensitivity, specificity, positive predictive value, and negative predictive value were then calculated accordingly. RESULTS Our review of 477 idiopathic scoliosis surgeries monitored using SSEPs alone revealed a new deficit rate of 0.63% with no cases of permanent injury. Sensitivity = 95.0%, specificity = 99.8%, positive predictive value = 95%, negative predictive value = 99.8%. Using evidence-based epidemiologic measures, we calculated that the number needed to treat was 1,587 patients for one intervention to be performed that would have been missed by SSEP monitoring alone. In addition, the number needed to harm, which represents the increase in false positives with the addition of transcranial electrical motor-evoked potentials, was 200. CONCLUSION SSEP monitoring alone during idiopathic scoliosis continues to be a highly reliable method for the detection and prevention of iatrogenic injury. Our results confirm the high sensitivity and specificity of SSEP monitoring alone published in earlier literature. As such, we suggest the continued use of SSEP alone in idiopathic scoliosis surgeries. At this time we do not believe there are sufficient data to support the addition of MEP monitoring, although more studies and revised criteria for the use of MEP may provide added value for its use in the future.

Extraction of Sources of Tremor in Hand Movements of Patients With Movement Disorders

This paper proposes an efficient method to acquire sources of tremor in patients with movement disorders based on blind source separation of convolutive mixtures. The extracted sources indicated neural activities that might be generated in the central nervous system. Four patients with essential tremor were tested in a set of movement tasks. Subjects wore a data glove that measured finger movements of the hand. The experimental data were then fed to a convolutive-mixture model, which revealed sources that imbibed in them the tremor frequency components of 2--8 Hz. Time--frequency analysis of these sources might be of potential help to clinicians to devise tasks that can manifest visible tremor from patients.