Shinichirou Taniguchi

Effects of experimental focal compression on excitability of human median motor axons

OBJECTIVE To characterize the effect of focal compression by threshold tracking and other excitability measures of human median motor axons. METHODS We conducted a sequence of excitability studies using a software written in BASIC (QTRAC version 4.0, (c)Institute of Neurology, London, UK, with multiple excitability protocol TRONDXM 2) in 24 healthy subjects, stimulating the median nerve at the wrist and recording compound muscle action potentials from the abductor pollicis brevis. Constant, localized compression was applied at the wrist by mechanically lowering a probe attached to a disk electrode, which also served as the stimulating cathode. RESULTS Compared with the pre-compression values, measurements during compression showed a shift of threshold electrotonus waveforms toward the baseline (fanning-in), steeper current-threshold relationships, increased strength-duration time constants, prolonged relative refractory periods and reduced levels of superexcitability, but no alteration in late subexcitability. These excitability changes indicating depolarization reversed to hyperpolarization immediately after release of compression. The nerve compression altered none of the excitability measures when recorded 2 cm distally from the pressure probe. CONCLUSIONS Mild nerve compression produces a very localized axonal depolarization at the compression site followed by hyperpolarization upon release of compression, as expected from focal ischemia. SIGNIFICANCE The current results imply that the sharply-localized conduction abnormalities demonstrated electrophysiologically in peripheral nerve entrapment syndromes and compression myelopathies may, in part, result from compression-induced focal nerve ischemia.

Incidence and Risk Factors of Postoperative Delirium in Cervical Spine Surgery

Study Design. Retrospective clinical review and prospective report of postoperative delirium after cervical spine surgeries. Objective. To investigate factors contributing to the development of delirium after cervical surgery and see whether amended therapeutic protocols could improve or alter postoperative outcomes. Summary of Background Data. Important consequences of postoperative delirium for the orthopedic patients include impaired recovery and increased morbidity and mortality. Although its risk factors have been reported in orthopedic surgery, there are a very few reports regarding postoperative delirium in spine surgery. Methods. Eighty-one cervical myelopathy patients were retrospectively examined about the incidence of postoperative delirium and the risk factors. Similarly, 41 patients who received postoperative care under modified protocols were prospectively examined. Results. Postoperative delirium occurred more commonly in patients over 70 years and those with hearing impairment. Patients who received high-dose methylprednisolone (>1000 mg) demonstrated an increased incidence of postoperative delirium. Under modified protocol, we reduced the usage of methylprednisolone and encouraged free body movement with cervical orthosis immediately after surgery. The incidence of postoperative delirium was significantly lower under the modified protocol. Conclusion. Early commencement of mobilization after cervical spine surgery would be crucial to the prevention of postoperative delirium in the elderly.

Visualization of Painful Experiences Believed to Trigger the Activation of Affective and Emotional Brain Regions in Subjects with Low Back Pain

In the management of clinical low back pain (LBP), actual damage to lower back areas such as muscles, intervertebral discs etc. are normally targeted for therapy. However, LBP may involve not only sensory pain, but also underlying affective pain which may also play an important role overall in painful events. Therefore we hypothesized that visualization of a painful event may trigger painful memories, thus provoking the affective dimension of pain. The present study investigated neural correlates of affect processing in subjects with LBP (n = 11) and subjects without LBP (n = 11) through the use of virtual LBP stimuli. Whole brain functional magnetic resonance imaging (MRI) was performed for all subjects while they were shown a picture of a man carrying luggage in a half-crouching position. All subjects with LBP reported experiencing discomfort and 7 LBP subjects reported experiencing pain. In contrast to subjects without LBP, subjects with LBP displayed activation of the cortical area related to pain and emotions: the insula, supplementary motor area, premotor area, thalamus, pulvinar, posterior cingulate cortex, hippocampus, fusiform, gyrus, and cerebellum. These results suggest that the virtual LBP stimuli caused memory retrieval of unpleasant experiences and therefore may be associated with prolonged chronic LBP conditions.

Effect of motion imagery to counter rest-induced suppression of F-wave as a measure of anterior horn cell excitability

OBJECTIVE To test if motor imagery prevents the rest-induced suppression of anterior horn cell excitability. METHODS Ten healthy subjects underwent two separate experiments, each consisting of stimulating the median nerve 100 times and recording F-waves from abductor pollicis brevis (APB) in three consecutive sessions: (1) after muscle exercise to standardize the baseline, (2) after immobilization of APB for 3h and (3) after muscle exercise to check recovery. We instructed the subject to volitionally relax APB in experiment 1 (relaxation task), and to periodically simulate thumb abduction without actual movement in experiment 2 (imagery task). RESULTS F-wave persistence and amplitude declined after relaxation task and recovered quickly after exercise, but changed little with imagery task. F-wave latencies showed no change when analyzed individually. The frequency distribution of collective F-waves recorded from all subjects remained the same after relaxation task, but showed a shift toward longer latencies after imagery task. CONCLUSIONS Mental imagery without overt motor output suffices to counter the effect of sustained volitional muscle relaxation, which would, otherwise, cause a reversible reduction in anterior horn cell excitability. SIGNIFICANCE This finding documents the importance of central drive for spinal excitability, which affects F-wave studies of a paretic muscle.

Virtual Pain Stimulation of Allodynia Patients Activates Cortical Representation of Pain and Emotions: A Functional MRI Study

Summary:The present study investigated neural correlates of affect processing in allodynia patients (n=8) and healthy controls (n=12) with the aid of virtual tactile stimulation. Whole brain functional magnetic resonance imaging was performed for allodynia patients and healthy volunteers while they were shown a video demonstrating light stimulation of the palm and another stimulation aimed at producing anticipation of palm stimulation. Contrasting with controls, patients displayed activation of the cortical areas related to pain and emotions: prefrontal cortex (Brodmanns area BA 10) and anterior cingulate cortex (BA 24). These findings may indicate involvement of an emotional component of pain perception in all odynia patients.

Functional importance of degenerative spondylolisthesis in cervical spondylotic myelopathy in the elderly.

Study Design. A correlation was studied between degenerative spondylolisthesis (DSL) of the cervical spine and spinal-evoked potentials intraoperatively recorded in elderly patients who had surgical treatment for cervical spondylotic myelopathy. Objective. To investigate the functional importance of cervical DSL in elderly patients with cervical spondylotic myelopathy. Summary of Background Data. Cervical DSL has received insufficient attention in contrast to the lumbar DSL. The authors are unaware of any journal article in which this condition has been evaluated electrophysiologically. Methods. This study investigated 47 patients with 68 DSL of 2 mm or more (3.1 ± 0.9 mm; range, 2–6 mm) who underwent serial intervertebral recording of spinal-evoked potentials from either the intervertebral disc or the ligamentum flavum after epidural stimulation. Results. All the study patients had unequivocal evidence of a focal conduction block, with the area of negative evoked potential peak reduced to less than 60% that of the immediately caudal level: 31 at C3–C4, 12 at C4–C5, and 1 each at C1–C2, C2–C3, C5–C6, and C6–C7. The site of conduction block matched the level of DSL in 30 patients, but not in 17 patients. The DSL accompanied by conduction block had significantly greater displacement with greater angular mobility than that without conduction block. Conclusions. A significant association between DSL and conduction block in the face of a relatively wide canal indicates the functional importance of DSL in elderly patients with cervical spondylotic myelopathy. In this age group, a high incidence of both DSL (81%) and focal conduction block (91%) at the upper cervical level (C3–C4 or C4–C5) is of clinical interest.

Motor-Evoked Potentials Elicited From Human Erector Spinae Muscles by Transcranial Magnetic Stimulation

STUDY DESIGN The compound muscle action potentials elicited from the erector spinae muscles by transcranial magnetic stimulation was studied in 15 healthy adults. OBJECTIVE To describe the recording procedure for consistent compound muscle action potentials elicited from the human erector spinae by transcranial magnetic stimulation and to establish the normal latency ranges of the responses, at respective spinal levels, for the practical use of this test. SUMMARY OF BACKGROUND DATA Although recording of the compound muscle action potentials from limb muscles after transcranial magnetic stimulation has been extensively studied, the use of the erector spinae as the target muscle has not, probably because of the difficulty of consistently evoking compound muscle action potentials. METHODS Compound muscle action potentials from the erector spinae muscles were recorded with the subject prone during tonic voluntary background contraction of the back extensor muscles at approximately 20% of maximum effort. The compound muscle action potentials were recorded concurrently at multiple levels after magnetic stimulation to the brain with a round coil centered over the vertex. RESULTS The onset and peak latencies (mean +/- SD) of the major negative potential increased progressively toward the caudal level from 13.4 +/- 2.2 msec and 17.6 +/- 2.2 msec at T5-T6 to 20.8 +/- 1.5 msec and 26.3 +/- 3.0 msec at L4-L5 in healthy subjects. The latencies changed significantly between two adjacent segments from T5-T6/T6-T7 through T12-L1/L1-L2. CONCLUSIONS The compound muscle action potential was elicited from the voluntarily contracted erector spinae at all spinal levels from T5-T6 through L4-L5 in all subjects tested. This noninvasive test has potential for evaluating the functional integrity of the motor pathway in the thoracic spinal cord, the spinal nerves, or both.

Rest-induced suppression of anterior horn cell excitability as measured by F waves: Comparison between volitionally inactivated and control muscles

To test the hypothesis that the anterior horn cells become hypoexcitable in the absence of central drive, we recorded F waves simultaneously from the first dorsal interosseous (FDI) and the abductor digiti minimi (ADM) before and after volitionally inactivating one muscle (target) while periodically contracting the other muscle (control). In 14 healthy subjects, F waves recorded from the target muscle showed a progressive decrease in persistence and amplitude (whether counting all 100 trials or only detectable responses) after muscle relaxation for 1, 3, and 6 hours, followed by a quick recovery upon brief muscle contraction. We conclude that volitional inactivation suppresses the F waves of the target muscle without equally affecting the control muscle innervated by the same nerve. The history of activity of a muscle should therefore be taken into account in clinical testing, especially when the study of a paretic muscle shows abnormal F‐wave excitability. Muscle Nerve, 2007

Virtual needle pain stimuli activates cortical representation of emotions in normal volunteers

Psychological factors are known to play an extremely important role in the maintenance and development of chronic pain conditions. However, it is unclear how such factors relate to the central neural processing of nociceptive transmission in healthy individuals. To investigate this issue, the activation of the brain was studied in 30 healthy volunteers responding to virtual pain stimuli by fMRI. In the first series of the study (non-preconditioned study), 15 participants were shown a digital video demonstrating an injection needle puncturing the right palm. In the second series of the study (pre-conditioned study), same-task paradigms were used for another 15 participants. Prior to the fMRI session, real needle punctuate stimuli were applied to the right palm of participants for pre-conditioning. fMRI analysis revealed that bilateral activations in anterior insula (BA45), parietal operculum (S2: BA40), premotor area, medial globus pallidus, inferior occipital gyrus (BA18), left temporal association cortex, right fusiform gyrus, right parietal association cortex and cerebellum occurred due to the task in the preconditioned group. On the other hand, right parietal operculum (S2: BA40), premotor area, parietal association cortex, left inferior frontal gyrus and bilateral temporal association cortex were activated in the non-preconditioned group. In addition, activation of anterior insula, inferior frontal gyrus, precentral gyrus and cerebellum significantly increased in the preconditioned group compared with the non-preconditioned group. These results suggest that the virtual needle puncture task caused memory retrieval of unpleasant experiences which is possibly related to empathy for pain, resulting in the activation of specific brain areas.

Effect of motor imagery and voluntary muscle contraction on the F wave.

We tested the validity of instructing patients to minimally contract the muscle to facilitate F‐wave recording in clinical practice. In 12 healthy subjects, F waves were recorded from the first dorsal interosseous muscle at rest, during motor imagery, and at up to 30% of the maximal voluntary contraction (MVC). F‐wave persistence increased significantly from 32.5 ± 11.9% (mean ± SD) at rest to 58.3 ± 15.2% during motor imagery and 90.0 ± 8.7% during 3% MVC. It then remained the same during stepwise changes to and from 30% MVC before decreasing significantly from 80.8 ± 18.5% during 3% MVC to 48.7 ± 23.8% during motor imagery and 27.0 ± 16.0% at rest. The trial average of F‐wave amplitude showed a similar pattern of facilitation. Motor imagery enhances F‐wave persistence and amplitude, which further increase with a slight muscle contraction and show no additional change with a stronger effort. Muscle Nerve, 2010