Short latency somatosensory evoked potentials during active hand movements

This study was designed to investigate the effect of active movement on spinal and cortical evoked responses. During voluntary hand movements the cervical and cortical short latency somatosensory evoked potentials (SEP) elicited by stimulation of the median nerve at the wrist were studied in nine healthy subjects. The latencies of the SEPs were not affected by active movements whereas the peak to peak amplitudes of the main cervical (N13-P15) and the main cortical (N20-P25) deflections were significantly reduced. The cortical subcomponents (N16 and N17), probably reflecting thalamic and thalamocortical activity, were not significantly affected by movements. The amplitude reductions in the cervical and cortical recordings might be related to proprioceptive feedback from the muscle afferents.     

听觉诱发电位N1-P2的强度依赖性

近年来的研究证明听觉诱发电位NI-P2的强度依赖性极有可能受到脑内5-HF抑制性神经元功能的调控,而NI的幅度和潜伏期又可以指示大脑皮层的唤醒水平。这些指标对失眠、头痛或心理障碍患者、或正常老年人的大脑感知状态有较高的参考价值。而在国内,尚无这方面的报道。为了此项研究能向临床拓展,我们在一批正常人中作了测试,旨在确立相关的正常值。八十三位受试者(47位女性和36位男性)被邀参加听觉诱发电位测试,刺激为四种不同强度70,80,90和100dB的clicks.这些chcks是按大约为0.5秒的刺激间隔而随机发放,这种间隔可引发出一个义务性的(obligatory)NI亚成份,而这个义务性NI常常表示受试者的唤醒状态或内在的注意力。P2的潜伏期在最高刺激理量时显著延长。NI-P2的峰对峰幅度和N1,P2的基线对峰的幅度都有显著的刺激强度依赖性,大多数受试者是“放大者”(augmenter)。本研究在幅度/刺激强度函数斜率和N1,P2的潜伏期等多项指标上确立了正常值。     

Detection of subclinical brain dysfunction by sensory evoked potentials in patients with severe diabetic ketoacidosis

Objective: Subclinical brain dysfunction is a potentially deleterious complication of diabetic ketoacidosis but is rarely recognized. Thus, we investigated the diagnostic value of sensory evoked potentials for detecting subclinical brain dysfunction in patients with diabetic ketoacidosis. Design: Prospective trial. Setting: Intensive care unit in a university hospital. Patients: 5 neurologically asymptomatic patients (Glasgow Coma Scale score 15, slight drowsiness; aged 20 to 66 years) with an established diagnosis of severe diabetic ketoacidosis were studied. Measurements and results: Short- and long-latency sensory evoked potentials were recorded within 2 h of initiation of therapy for ketoacidosis and 7 days after normalization of ketoacidosis, respectively. Two hours after starting therapy, sensory evoked potential peak latencies were prolonged in all five patients compared to age-matched healthy subjects [cervical N 13 to cortical N 20 interpeak latency of short-latency evoked potentials (mean) 5.8 vs 5.3 ms, p < 0.05; N 35 peak latency 40 vs 34 ms, p < 0.05; N 70 peak latency of long-latency evoked potentials 102 vs 76 ms, p < 0.01]. In all five patients, cervical N 13 to cortical N 20 interpeak latency and N 35 and N 70 peak latency reverted to normal 7 days after recovery from diabetic ketoacidosis. Conclusions: Our study indicates that the recording of sensory evoked potentials is a sensitive method of detecting subclinical brain dysfunction in patients with severe diabetic ketoacidosis. Since sensory evoked potentials were significantly prolonged in all five patients, this strongly suggests that subclinical brain dysfunction occurs more frequently than is generally recognized.     

糖尿病性神经病的体感诱发电位分析

对２６例Ⅱ型糖尿病患者进行体感诱发电位（ＳＥＰ）检测,以了解其神经病变（ＤＮＰ）情况。结果：依临床表现诊断有工发症患者５４％,ＳＥＰ异常７６．９％,其中上肢异常５０％,下肢异常９０％。主要表现为上肢Ｎ９和下肢Ｐ４０潜伏期明显延长,Ｎ９平均峰潜伏期男１２．３ｍｓ,ｓ：０．８６,Ｐ〈０．００１,女分别为１１．６ｍｓ,０．８８,Ｐ〈０．００２;Ｐ４０平均峰值伏期男４５．７ｍｓ,ｓ：４．５５,Ｐ〈０．００     

Epidural anesthesia in surgical interventions on the spine and spinal cord. II. Effects of epidural anesthesia on somatosensory evoked potentials

Effects of epidural anesthesia (EA) on early components of somatosensory evoked potentials (SSEP) were studied and the objectiveness and efficiency of SSEP monitoring during interventions on the spine under EA were evaluated. Evoked potentials were studied in 21 patients operated on for vertebral disk hernias and extra-intradural tumors of the spine (lower thoracic and lumbar levels) under bupivacaine EA. Cortical SSEP were recorded and analyzed on a Viking IV neuroaverager (Nicolet, USA) stimulating n. tibialis posterior for obtaining a greater amplitude of evoked potentials. The following SSEP characteristics were measured: latency of PI (P37), NI (N45), and PII (P60) peaks, amplitude of PINI peak, and inter-peak latency of PI-NI and PI-PII. The major changes in cortical SSEP caused by EA (local anesthetic 0.5% bupivacaine) involve only PI and NI components which reflect the entry of information on an external stimulus into the cortex and objective physical parameters of this stimulus; this helps predict the onset of full-value epidural block and its duration. General anesthetic (propofol) affect mainly a later component of response, PII peak, which is responsible for processing of primary information about an external stimulus and reflects the activation of associative areas of the brain. Hence, SSEP regulation can be used together with traditional methods (pin prick test and Bromage scale) for evaluating epidural block in patients with spinal diseases.     

健康人磁刺激膈肌运动诱发电位初探

目的　探讨经颅磁刺激膈肌运动诱发电位 (diaphragmaticmotorevokedpotential,DMEP)在健康人群中的电生理学特点。方法　分别经项部及经颅部磁刺激 3 1例 (共 61侧 )健康志愿者 ,并用皮肤表面电极记录各受检者的DMEP ,并分析其电生理学特点。结果　所有受检者在深吸气易化时 ,均可引出DMEP ;右侧颈潜伏期大于左侧 ,皮层潜伏期、颈潜伏期与身高呈正相关 ,中枢运动传导时间 (centralmotorconductiontime ,CMCT)不受侧别、性别、年龄、身高等因素影响 ;本组受检者左侧颈潜伏期为 ( 7.8± 0 .6)ms ,右侧颈潜伏期为 ( 8.3± 0 .6)ms ;合并不同侧别及性别后皮层潜伏期为 ( 12 .2± 1.0 )ms ,CMCT为 ( 4 .1± 0 .7)ms。结论　DMEP是评价与呼吸有关的皮质脊髓束功能的重要电生理学指标之一。     

Pelvic restraint effect on lumbar gluteal and hamstring muscle electromyographic activation

OBJECTIVE: To evaluate the influence of pelvic restraint on electromyographic activation (neural drive) of the lumbar extensor, gluteal, and hamstring muscles during submaximal dynamic lumbar extension in an upright seated position. DESIGN: Randomized, balanced, crossover trial comparing the electromyographic activation of the lumbar, gluteal, and hamstring muscles during dynamic lumbar extension exercise with and without pelvic restraint. SETTING: Research laboratory at a private research university. SUBJECTS: Twelve apparently healthy men (ages 18 to 50 yrs). INTERVENTION: Dynamic lumbar extension exercises. MAIN OUTCOME MEASURE: Electromyographic recordings. RESULTS: Pelvic restraint did not influence the relative activation of the lumbar, gluteal, or hamstring muscle groups (p< or =.05) during submaximal dynamic lumbar extension exercise. The relative activation of the gluteal muscles was significantly lower than that of the lumbar extensor and hamstring muscle groups. CONCLUSIONS: Pelvic restraint is not a requirement to promote neural drive to the lumbar musculature during submaximal dynamic lumbar extension exercise performed in an upright seated position. Submaximal lumbar extension exercise reduces the relative contribution of the gluteal muscles compared with a maximal voluntary isometric contraction.     

Cortical somatosensory evoked potentials: effects of positional changes

Supine and sitting lower extremity cortical somatosensory evoked potential (CSEP) examinations were performed in 30 healthy volunteers to establish normal values and to determine variations in SEP parameters caused by positional changes, side of stimulation, and the influence of height. CSEPs were recorded at Cz'-Fz (10-20 international EEG system) after stimulation of the saphenous, peroneal, and sural nerves at the ankle. Each nerve was tested in the supine and sitting positions. CSEP P1, N1 latencies and P1 - N1 amplitudes were recorded. The mean values of these parameters and side-to-side differences were determined for both positions. Parameter changes between the two positions were also determined. No statistically significant difference was found when comparing supine and sitting, or side-to-side values (p greater than 0.05). Regression analyses of P1 latency vs height revealed a significant positive correlation for both positions (p less than 0.0001-0.0045). Mean P1 and N1 latencies (msec) +/- 1SD, and mean P1 - N1 amplitudes (microV) +/- 1SD are as follows: peroneal nerve (n = 119) P1 = 39.5 +/- 2.98, N1 = 48.2 +/- 3.79, P1 - N1 = 1.41 +/- 0.81; sural nerve (n = 119) P1 = 41.3 +/- 4.03, N1 = 50.9 +/- 4.57, P1 - N1 = 1.31 +/- 0.61; saphenous nerve (n = 119) P1 = 41.5 +/- 4.02, N1 = 50.4 +/- 4.10, P1 - N1 = 0.87 +/- 0.30. The normative data generated by this study will help clinicians to distinguish normal variations in lower extremity CSEP parameters.(ABSTRACT TRUNCATED AT 250 WORDS)     

模拟腰椎间盘髓核摘除后疲劳载荷对腰椎稳定性的影响

背景：腰椎间盘髓核摘除术后何时下床活动目前尚无统一标准,实验拟通过腰椎间盘髓核摘除术后早期的生物力学变化来指导患者进行功能锻炼。目的：观察腰椎间盘髓核摘除后疲劳载荷对腰椎稳定性的影响。方法：取3具新鲜猪脊柱标本,制成12个脊柱功能单位,随机分为A,B,C组,行单侧椎板开窗髓核摘除后,在不同循环载荷压力（500～1000N,500～2000N,500～3000N）下行疲劳载荷实验。结果与结论：A,B组椎间盘高度、刚度差异无显著性意义（P〉0.05）,应变增大差异有显著性意义（P〈0.05）;B,C组椎间盘高度和刚度的降低、应变的增大差异均有显著性意义（P〈0.01）。循环载荷后3组间比较,椎间盘高度、应变、刚度的变化幅度均随载荷压力的增大而变大（P〈0.05）。结果说明髓核摘除后较大的载荷会破坏腰椎的稳定性。     

Comparison of tibial nerve H-reflex excitability after cervical and lumbar spine manipulation

BACKGROUND: Previous investigations indicate that spinal manipulation leads to short-term attenuation of alpha-motoneuron excitability, when assessed by means of the Hoffmann reflex. Past studies, however, are limited to regional effects, such as lumbar manipulation effects on lumbar alpha-motoneuron activity. OBJECTIVE: This study compared and contrasted the effects of cervical and lumbar spine manipulation on the excitability of the lumbar alpha-motoneuronal pool in human subjects without low back pain, and compared the effects of cervical (nonregional) and lumbar (regional) spinal manipulation on lumbar alpha-motoneuron pool excitability in healthy subjects. The specific aim of this study was to determine if the inhibitory effects on the lumbar alpha-motoneuron pool associated with spinal manipulation are limited to the specific region in which the manipulative procedure is applied, or if rostral (cervical) manipulation can also influence caudal (lumbar) motoneuron excitability. METHOD: Thirty-six nonpatient human subjects were used to study the effect of cervical and lumbar spinal manipulation on the amplitude of the tibial nerve Hoffmann reflex, recorded from the gastrocnemius muscle. The Hoffmann reflex (H-reflex) technique allows for an indirect index of motoneuron pool excitability by means of peripheral nerve Ia-afferent fiber stimulation. Reflexes were recorded before and after spinal manipulative procedures. RESULTS: Lumbar spinal manipulation, as measured by amplitude changes of the tibial nerve H-reflex, attenuated lumbar alpha-motoneuronal activity. Suppression of motoneuronal excitability was significant (P <.05) but transient, with a return to baseline within 60 seconds after manipulation. Cervical spinal manipulation had no significant effect on lumbar motoneuron activity. CONCLUSION: These data indicate that the inhibitory effects of spinal manipulation on motoneuronal excitability are regional, rather than global.     

How do elliptical machines differ from walking: a study of torso motion and muscle activity

Background

The elliptical trainer is a popular exercise modality, yet its effect on the lumbar spine is poorly understood. The purpose of this study was to analyze the effect of different hand positions, speed and stride lengths on spine kinematics and corresponding muscle activity while using the elliptical trainer, and compare with those demonstrated in normal walking.

Methods

Electromyographic data was collected over 16 trunk and gluteal muscle sites on 40 healthy males (mean age (SD) = 23(3)) while on the elliptical trainer. Two stride lengths (46, 66 cm), 2 speeds (self-selected, 30% faster), and 3 hand positions (freehand, central bar, handles) were analyzed. Lumbar spine kinematics was calculated from data collected using a motion capture system. Results were compared to those found in walking using repeated measures ANOVA for each dependent variable with Bonferroni adjustments (P < 0.004. Correlations were made between lumbar motion and various anthropometric measures.

Findings

All significance levels comparing walking to elliptical varied according to stride length, speed and hand position. Average lumbar flexion angles and lumbar rotation were generally greater on the elliptical trainer, whereas walking produced more frontal motion. Total lumbar flexion/extension was similar between the two activities. Muscle activation patterns of the gluteal muscles were consistently higher on the elliptical, whereas the back extensors, latissimi and internal obliques were greater in only selected conditions.

Interpretation

The various hand positions, speeds and stride lengths affect lumbar motion and muscle activity on the elliptical trainer, thus must be considered when incorporated into an exercise protocol.     

Prefrontal transcranial magnetic stimulation produces intensity-dependent EEG responses in humans

The reactivity of the prefrontal cortex (PFC) was studied by measuring electroencephalographic (EEG) responses to transcranial magnetic stimulation (TMS) with different stimulus intensities. Focal TMS at intensities of 60%, 80%, 100%, and 120% of the motor threshold was delivered to the left middle frontal gyrus identified individually from magnetic resonance images (MRI) in seven healthy subjects. EEG was simultaneously recorded with 60 scalp electrodes. Stimulation evoked clear responses at all intensities. Left prefrontal TMS evoked an averaged EEG response consisting of five deflections at 27 +/- 3 ms (peak I), 39 +/- 3 ms (II), 52 +/- 7 ms (III), 105 +/- 14 ms (IV), and 193 +/- 15 ms (V) at the Fz/FCz electrodes. The slope of the almost linear dependence of the overall response on stimulus intensity varied with latency. Potential distributions were relatively similar for the four intensities, suggesting that the same cortical structures may be activated. Intensity dependence function to TMS may be an indicator of cortical activation in humans.     

Recovery of spinal cord conduction after surgical decompression for cervical spondylotic myelopathy: serial somatosensory evoked potential studies

OBJECTIVE: We tested the utility of scalp-recorded median and tibial somatosensory evoked potentials (SEPs) as a measure of delineating the time course of postoperative recovery from cervical spondylotic myelopathy. DESIGN: We evaluated serial median and tibial SEP studies for 20 hands and 22 feet in 13 cervical spondylotic myelopathy patients during the first 6 mo postoperatively or longer. Serial sensory assessment of the hands and feet served to evaluate clinical correlation with the SEPs. RESULTS: The studies distinguished three recovery patterns of the SEPs based on the time course of the latencies of the N20 component for the median SEP and the P40 component for the tibial SEP. The latency started to decrease by 0.5 msec or more within 2 wk (seven hands and eight feet) or later than 2 wk (six hands and eight feet) postoperatively, or the change did not reach 0.5 msec (seven hands and six feet). In the late recovery group, the SEP improvement began as late as 10 wk postoperatively. Sensory recovery correlated with the SEP change in every group. CONCLUSIONS: An early onset of the SEP recovery predicts a favorable clinical course. The SEP may begin to improve later, and once it occurs, progressive return of function will follow.     

体位及康复运动疗法在颈腰椎间盘患者中的应用

目的探讨体位及康复运动疗法在颈腰椎间盘患者中的应用价值。方法选取140例颈腰椎间盘患者随机分为观察组和对照组各70例,对照组采用针灸、药物及牵引为主的常规对症治疗,观察组在此基础上采用规律的体位及康复运动疗法,评价2组临床疗效、颈腰椎疼痛程度、腰椎功能及颈腰椎活动度。结果观察组临床总有效率为87.14%,高于对照组的72.86%(P0.05);治疗前,2组视觉模拟疼痛(VAS)评分、腰椎功能障碍指数(ODI)评分差异无统计学意义(P0.05),治疗后,2组评分均显著降低,且观察组VAS评分、ODI评分低于对照组(P0.05);治疗前,2组颈椎前屈、后伸活动度和腰椎屈伸、旋转活动度差异无统计学意义(P0.05),治疗后,2组均显著改善,且观察组颈椎前屈、后伸活动度和腰椎屈伸、旋转活动度均高于对照组(P0.05)。结论体位及康复运动疗法辅助对症治疗颈腰椎间盘患者疗效满意,对缓解疼痛和改善颈腰椎活动度有重要的临床价值。     

Timing of early activity in the visual cortex as revealed by simultaneous MEG and ERG recordings

To clarify the latency of the earliest cortical activity in visual processing, electroretinograms (ERGs) and visual evoked magnetic fields (VEFs) following flash stimulation were recorded simultaneously in six human subjects. Flash stimuli were applied to the right eye and ERGs were recorded from a skin electrode placed on the lower lid. ERGs showed two major deflections in all subjects: an eyelid-negativity around 20 ms and a positivity around 60 ms corresponding to an a- and b-waves, respectively. The mean onset and peak latency of the earliest component of VEFs (37 M) was 30.2 and 36.9 ms, respectively. There was a linear correlation between the peak latency of the a-wave and the onset latency of the 37 M (r=0.90, P=0.011). When a single equivalent current dipole analysis was applied to the 37 M, four out of six subjects showed highly reliable results. The generator of the 37 M was estimated to be located in the striate cortex in all four subjects. Since post-receptoral activities in the retina are expected to start around the peak of the a-wave (20 ms), the early cortical activity, which appears 10 ms later than the a-wave peak, is considered to be the earliest cortical activity following flash stimulation.     

Vagal afferent fibers excite upper cervical neurons and inhibit activity of lumbar spinal cord neurons in the rat.

Effects of electrical stimulation of the cervical vagus nerve were determined in cervical or lumbar spinal neurons in 27 rats anesthetized with pentobarbital. Ipsilateral cervical vagus stimulation (ICVS) increased activity of 44 neurons in the C1 segment. At the same stimulation parameters, contralateral cervical vagus stimulation (CCVS) either increased, decreased or did not affect activity of C1 neurons that were excited by ICVS. For C1 cells excited by both ICVS and CCVS, the mean latency for activation was significantly longer for CCVS than for ICVS, and ICVS produced a greater degree of excitation than CCVS. In segments C2-C6, 16 of 18 neurons were excited by ICVS and 2 were inhibited. However, CCVS did not excite the C2-C6 neurons but either inhibited or did not affect activity. In 6 cervical cells, a CCVS conditioning stimulus reduced the level of excitation by ICVS (test stimulus). Transection of the C2 or C3 dorsal roots did not significantly affect the excitatory vagal input to C1 cells. Excitatory somatic receptive fields were classified for 60 cervical spinal cells that responded to vagal stimulation. Most (87%) cells were excited by noxious pinch; 29 were wide dynamic range (WDR) cells and 21 were high threshold cells. In contrast to upper cervical neurons, spinothalamic tract (STT) and spinal cells in lumbar segments were not excited by ICVS or CCVS at the stimulation parameters used in this study, but were primarily inhibited by vagal stimulation. Results of this study showed that a group of cells in upper cervical segments were excited by vagal afferents. This excitatory vagal input reaches the C1 segment primarily via an ipsilateral, supraspinal route.     

Electrophysiological assessment of the afferent sensory pathway in cardiac arrest survivors

BACKGROUND: Hypoxic-ischaemic brain damage in cardiac arrest survivors is global, but postmortem histology could identify parts of the brain that are selectively vulnerable to ischaemia, comprising the thalamus and cortex. We hypothesized that hypoxic-ischaemic brain damage increases along the afferent sensory pathway with a stepwise decrease of detectable somatosensory evoked potential peaks. METHODS: Somatosensory evoked potentials were recorded within 72 h after cardiac arrest in 305 comatose patients after cardiopulmonary resuscitation. We measured the short latency SEP peaks N9, P15, N20, P25 (reflecting the peripheral-thalamo-cortical pathway) and the long latency SEP peaks N35 and N70 (reflecting complex cortico-cortical interactions). Patients with a Cerebral Performance Category score > 2 at 1 year were defined as patients with hypoxic-ischaemic brain damage. RESULTS: Patients with hypoxic-ischaemic brain damage (n = 232) showed a statistically significant decrease of detectable peaks (P < 0.05) along the thalamo-cortical afferent pathway: N13, P15, N20, P25 and N70 peaks were detectable in 99%, 63%, 59%, 55% and 44% patients, respectively. In patients without hypoxic-ischaemic brain damage (n = 73) the N13, P15, N20, P25 peaks were detectable in all, and the N35 and N70 peaks in 98%. Furthermore, in patients with hypoxic-ischaemic brain damage and detectable SEP peaks, P15, N20, P25, N35 and N70, peak latencies were prolonged (P < 0.05) and N20 and N70 amplitudes were decreased (P < 0.05) compared with patients without hypoxic-ischaemic brain damage. CONCLUSION: Extent of hypoxic-ischaemic brain damage in cardiac arrest survivors increases along the afferent sensory pathway, with pronounced vulnerability of thalamic and cortical brain regions.     

Somatosensory evoked potential in general anesthesia

Somatosensory evoked potentials (SSEP) were investigated under general anaesthesia in 12 patients with no history of previous cerebral disease. With the commonly-used stimulation of the median nerve on the wrist, conduction from the homolateral Erb's point, and contralateral conduction from the mastoid and sensory cortical area, SSEP were registered during the first 100 msec. after the stimulation. Latency period, shape and amplitude of the spinal and subcortical components and early cortical potentials (N 20, P 28) show no change, whereas the consecutive negative and positive cortical SSEP show a definite change in shape and latency period. No change was registered in somatosensory impulse conduction and early cortical response under general anaesthesia and these can, therefore, be used during neurosurgery as a parameter for the control of cortical and subcortical functioning.     

Measuring the posteroanterior stiffness of the cervical spine

An essential part of improving manual therapy treatment for cervical spine disorders is the identification of the mechanical effects of manual techniques. The aims of this research were to develop a reliable and safe instrument for measuring cervical spine stiffness, and to document stiffness in a group of asymptomatic individuals. A device for measuring cervical spine stiffness was designed and tested. The stiffness of the cervical spine of 67 asymptomatic individuals was measured at C2 and C7 on one or more occasions. Stiffness was defined as the slope of the linear region of the force-displacement curve (coefficient K). For C2, the linear region of the force-displacement curve was from 7 to 40 N, and for C7, 20-70 N. The mean stiffness (coefficient K) on the first measurement occasion at C2 was 4.58 N/mm (95% CI 4.30-4.85), and at C7 was 7.03 N/mm (95% CI 6.50-7.57). ICC(2,1) for repeated measurements was 0.84 (95% CI 0.74-0.90). Stiffness measurements in the cervical spine were generally lower than those previously reported for the lumbar spine. Age was positively associated with C2 stiffness (p=0.01). Males were stiffer at C7 than females (p<0.001). This research provides a basis for future studies investigating the effects of manual techniques on cervical spine stiffness, potentially leading to improved outcomes for patients treated by manual therapy.     

Benzodiazepine tolerance, physical dependence and withdrawal: electrophysiological study of spinal reflex function

The in situ segmental spinal reflex system of the rat was used to determine changes in excitatory and inhibitory synaptic function associated with benzodiazepine tolerance, physical dependence and withdrawal. Rats were made physically dependent on chlordiazepoxide using a chronically equivalent dosing method. After spinalization, dorsal and ventral lumbar roots (L5 or L6) were isolated for extracellular stimulation and recording. Testing of spinal function was performed during peak withdrawal (8 days) and at peak effect (4 hr) after first ("acute") and last ("chronic") dose of chronically equivalent chlordiazepoxide. There were no quantitative or qualitative differences in the acute and chronic spinal actions of chlordiazepoxide. Polysynaptic discharges were markedly augmented during withdrawal (159% above control) and diminished during treatment (44% below control). Recovery of the 2 N reflex measured by twin pulse was shortened during withdrawal (23% above control) and lengthened during treatment (28% below control). Recovery of the 2 N reflex analyzed by low-frequency (10 Hz) stimulation was also elevated at peak withdrawal (40% above control) and depressed in treatment (41% below control). At peak withdrawal spinal inhibitions were reduced below control; presynaptic-dorsal root reflex (60%) and recurrent (62%). In contrast, drug treatment enhanced presynaptic (72%) and recurrent (48%) inhibitions above control. Only those synaptic parameters chronically altered by continuous chlordiazepoxide administration were oppositely affected during withdrawal. Consequently, benzodiazepine withdrawal is associated with rebound alterations of profound reductions in inhibitory synaptic transmission, increased net polysynaptic activity and shortened monosynaptic recovery times.