Comparison of somatosensory evoked responses from root and cord recorded by skin and epidural electrodes using stimulation of the median nerve in cervical radiculopathy and radiculomyelopathy

Somatosensory evoked potentials (SEPs) were recorded by stimulating the median nerve at the wrist from the skin and epidural space of the 7th cervical spine in patients suffering from cervical radiculopathy or radiculomyelopathy. The patients were divided into four subgroups according to the severity of the disease. Skin and epidural SEPs were calculated and compared with each other and with control values. Usually only one negative potential N13 was identified in the skin recording, but two potentials N11 and N13 occurred in the epidural recording. Lower amplitudes were obtained from the skin than from the epidural space. In the skin SEPs the mean of the central latency of N13 was significantly prolonged in the severe radiculomyelopathy groups, while the mean of the amplitude N13 showed only a tendency to decrease. In contrast, in the epidural SEPs a significant decrease in the mean of the N11 and N13 amplitudes together with a significant prolongation in the mean of the central latency of N13 could be found. In the epidural recording the amplitude changes in particular increased with the severity of the disease, but the highest number of abnormalities (61%) could be seen in the central latency of N13.     

Metastatic squamous cell carcinoma of the neck from an unknown primary: management options and patterns of relapse

PURPOSE: Management of squamous cell carcinoma of undetermined primary tumors in the head and neck region is controversial. Here we report the Southern California Kaiser Permanente experience with these patients. METHODS AND MATERIALS: From January 1969 through December 1994, 106 patients were eligible for this retrospective analysis. Distribution of nodal staging was as follows: 14 N1, 27 N2A, 39 N2B, 2 N2C, and 24 N3. Initial treatment included excisional biopsy alone in 12, radical neck dissection alone in 29, radiotherapy alone in 24, excisional biopsy followed by radiotherapy in 15, and radical neck dissection plus postoperative radiation in 26 patients. RESULTS: Except for two patients, all patients have had a minimum follow-up of 5 years. Overall, 57 patients (54%) have had recurrences. Only two patients (3%) who had received radiotherapy as part of their initial treatment had an appearance of a potential primary site inside the irradiated field vs 13 patients (32%) who had not received radiotherapy (p =.006). Combined modality therapy resulted in fewer neck relapses, particularly in patients with advanced neck disease. Including salvage, surgery alone as the initial treatment resulted in 81% ultimate tumor control above the clavicle for patients with N1 and N2a disease without extracapsular extension. The 5-year survival for the entire population was 53%. Radiotherapy alone resulted in poor survival in patients with advanced/unresectable neck disease. No significant difference in survival based on the initial treatment was found. The statistically significant adverse factors in determining survival included advanced nodal stage and the presence of extracapsular extension. CONCLUSIONS: Radiotherapy is very effective in reducing the rate of appearance of a potential primary site. However, in the absence of advanced neck disease (N1 and N2A without extracapsular extension), radiotherapy can be reserved for salvage. Radiotherapy alone results in poor outcomes in patients with advanced/unresectable neck disease, and incorporation of concurrent chemotherapy and cytoprotective agents should be investigated.     

Evoked potentials in the follow-up and prognosis of patients with craniocerebral trauma

The aims of this study were to find a reliable way of establishing the prognosis for the final outcome in the first week after head injury, to show the correlation between abnormalities in evoked potentials (EP) and clinical coma score, and finally, to document EP results in patients with the clinical diagnosis of brain death. We examined 46 patients, 23 in different states of coma and 23 with bulbar syndrome (complete absence of cortical and brain stem function). In the group of comatose patients brain stem auditory EP (BAEP) and somatosensory EP (SEP) were recorded in the first 48 h, 3-5 days, 1 week and 4 weeks after the head injury. The depth of coma was scaled with a scoring system devised by the authors and with the Innsbruck coma scale. Outcome was evaluated with the Glasgow outcome scale after 3, 6, and 9 months. BAEP were recorded bilaterally after stimulation with clicks; SEP were recorded from the neck (C2) and the contralateral cortex (C3', C4') after electrical stimulation of the median nerve. Evoked potentials were scored according to a four-point scale from grade 1 (normal) to grade 4 (only component I present in BAEP or absence of cortical responses on both sides in SEP). We found a significant correlation between the mean SEP score of the first week and the Glasgow outcome of the 3rd month, but no significant correlation between the BAEP score of the first week and the Glasgow outcome. There was a significant correlation between SEP (BAEP) scores and the corresponding clinical score.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of nitrous oxide on transcranial magnetic-induced electromyographic responses in the monkey

Transcranial magnetic stimulation (TMS) to produce motor evoked potentials (MEPs) is a newly developed intraoperative modality to monitor functional integrity of the motor pathways. The present study was designed to examine the reliability of magnetic MEP recording under nitrous oxide (N2O) inhalation. Following ketamine injection (10 mg/kg i.m.) and endotracheal intubation, 16 monkeys were exposed to N2O:O2 mixture ratios 1:3, 1:1, and 3:1. Electromyographic (EMG) responses, evoked by pulsed magnetic fields applied extracranially to the scalp zone overlying motor cortex, were recorded from the contralateral fore- and hind limb flexor muscles. The scalp topography zone for contralateral muscle excitation was markedly reduced by 75 vol% N2O. Significant stimulation threshold elevation, latency prolongation, and amplitude depression were noted after inhalation of 75 vol% N2O (p <0.05) compared with 相似文献   

Do somatosensory evoked potentials in traumatic brain injury patients indicate brainstem generators for frontally recorded N18, P20 and cervical N13?

Primary objective: To examine the generator of frontal somatosensory evoked potentials by studying patients with traumatic brain injury in the chronic phase. Research design: A prospective, non-comparative case series. Methods and procedures: Median nerve somatosensory evoked potentials were performed in 26 survivors of severe traumatic brain injury, which had taken place at a mean of 7 months before. Potentials of short latency somatosensory evoked potentials were recorded simultaneously over the frontal and parietal scalp. Main outcomes and results: Frontally recorded latencies N18, P20 and N13 recorded from C2 correlated highly significantly with the duration of coma (p<0.01), a history of raised intracranial pressure (p<0.05) and with each other (p<0.01) in traumatic brain injury patients. Conclusions: These findings indicate that frontally recorded N18, P20 and N13 recorded from C2 are generated in part in the brainstem, which becomes damaged by increased intracranial pressure due to secondary injury in severe traumatic brain injury.     

EFFECTS OF HALOTHANE AND ENFLURANE ON FAR AND NEAR FIELD SOMATOSENSORY EVOKED POTENTIALS

Somatosensory potentials evoked in response to median nervestimulation were studied in 10 patients during surgery undergeneral anaesthesia with halothane (five patients) or enflurane(five patients). Bipolar scalp responses (near field) and scalpto non-cephalic reference (far field) potentials were recordedbefore the induction of anaesthesia, and after 15 min stabilizationat each of 0.5, 1.0, 1.5 and 2.0% end-tidal concentrations ofanaesthetic agent. Both agents produced similar effects. Thelatency of the bipolar responses was increased and the amplitudedecreased. The amplitude of the far field, subcortically generated,potentials measured from the scalp to non-cephalic electrodesdid not decrease as much as the near field potential with increasingconcentrations of volatile anaesthetic, although the latencyof the potential recorded at the frontal electrode increased.At higher anaesthetic concentrations the virtual eliminationof the near field potential caused the frontal and rolandicpotentials to appear to be identical. Since far field somatosensoryevoked potentials are preserved during deep anaesthesia, theyshould be considered for use when measurement of evoked responsesis required sfor monitoring purposes.     

Causes of organ donation refusal in southern Iran

Background

Family refusal is an important factor that limits the number of organ donations. Some studies from different centers have reported various reasons for family decisions of organ donation refusal. This study evaluated the reasons for organ donation refusal by family members covered in our organ procurement organization.

Methods

This cross-sectional study was performed among families of potential organ donors who satisfied brain death criteria as identified between March 2009 and March 2010.

Results

Among 125 potential donors 73 (58.4%) families refused donation. Their main reasons were as follows: lack of acceptance of brain death n = 26 (35.6%), belief in miracle and patient recovery (n = 22; 30.1), fear of gossip regarding sale rather than autonomous organ donation (n = 11; 15.1%), and fear about deformation of the donor's body (n = 9; 12.3%).

Conclusion

Family members play an important role in the final decision for organ donation. The general public should be encouraged to register their donation preferences in the case of brain death.     

皮层体感诱发电位与脊髓型颈椎病患者脊髓功能相关性

目的研究皮层体感诱发电位(cortical somatosensory evoked potentials,CSEP)与脊髓型颈椎病(cervical spondylitic myelopathy,CSM)患者脊髓功能的相关性。方法 2008年7月—2012年5月在本院诊断为CSM的患者67例。记录CSM患者CSEP与颈段脊髓传导功能的相关指标,包括N13、N20潜伏期,N9~N20、N9~N13峰间潜伏期(interpeak latency,IPL),P13~N13、P20~N20峰-峰值(peak-peak amplitude,PPA)。记录患者日本骨科学会(Japanese Orthopaedic Association,JOA)评分。将CSEP记录值与JOA评分关系绘制成散点图,当观察到点分布有直线趋势,进行直线相关分析。结果 N9~N13 IPL与JOA评分呈显著负相关。N13潜伏期和N9~N20 IPL与JOA评分呈负相关。结论 N9~N13 IPL与CSM患者脊髓功能障碍程度显著相关,可作为CSM患者脊髓功能评估的电生理指标。     

吗啡对电刺激坐骨神经诱发大鼠脊髓背角突触长时程增强的影响

目的 评价吗啡对电刺激坐骨神经诱发大鼠脊髓背角突触长时程增强(LTP)的影响.方法 雄性SD大鼠27只,日龄60～90 d,体重180～200 g,随机分为4组:对照组(C组,n=7)、吗啡组(M组,n=7)、纳洛酮组(N组,n=6),纳洛酮+吗啡组(MN组,n=7).麻醉下分离左侧坐骨神经,记录电极插入左侧T13～L1脊髓背角,刺激电极刺激左侧坐骨神经,给予15 V、0.5 ms、1/60 Hz单个方波电刺激30 min以诱发场电位,抽取生理盐水10 μl、吗啡10 μl(15 μg/μl)、纳洛酮10 μl(2.5 μg/μl)、纳洛酮(2.5 μg/μl)和吗啡(15 μg/μl)各5 μl的混合液,在脊髓上方3～5 mm,经2 min内缓慢滴注,给药后5 min时,给予4串高频高强度强直电刺激后,再给予15 V、0.5 ms、1/60 Hz单个方波电刺激210 min,记录强直刺激前30 min、强直刺激后即刻～30 min、35～60 min、65～120 min、125～210 min时段平均场电位幅值及潜伏期.结果 与C组比较,M组和MN组平均场电位幅值降低,潜伏期延长(P<0.05或0.01),N组上述指标差异无统计学意义(P>0.05).与M组比较,MN组平均场电位幅值升高,潜伏期缩短(P<0.05或0.01).与强直刺激前30 min比较,C组和N组在强直刺激后各时段平均场电位幅值升高,潜伏期缩短,M组在强直刺激后各时段平均场电位幅值降低,潜伏期延长,MN组在强直刺激后即刻～30 min和35～60 min时段平均场电位幅值升高,强直刺激后即刻～30 min时段潜伏期缩短,65～120 min和125～210 min时段平均场电位幅值降低,潜伏期延长(P<0.05或0.01).结论 吗啡可抑制电刺激坐骨神经诱发大鼠脊髓背角突触LTP,可能是其抑制中枢敏化的机制之一.     

Nasopharyngeal electrode recording of somatosensory evoked potentials as an indicator in brain death

Median nerve somatosensory evoked potentials were recorded in 28 comatose patients, eight of whom were progressing from coma to eventual brain death and in 11 brain dead patients using electrodes over the scalp, neck and nasopharynx (nasopharyngeal electrode). This recording technique was used to assess the different derivation of brainstem P14 wave activity. It showed that in the midfrontal scalp to the nasopharynx derivation a clear P14 was present in all comatose patients. This component disappeared during the passage from coma to brain death. In a separate group, simultaneous direct recordings in the vicinity of the dorsal column nuclei and with a nasopharyngeal electrode were made in five patients undergoing neurosurgical procedures at the craniocervical junction with the same somatosensory evoked potential monitor. We found that the P14 recorded with the nasopharyngeal electrode in the neurosurgical patients corresponded in latency and morphology with the P14 recorded directly on the surface of the craniocervical junction and more specifically in the vicinity of the nucleus cuneatus. The nasopharyngeal electrode provides non-invasive access to the ventral brainstem at the medullo-pontine level and the disappearance of the P14 shows a clear sign of involvement of the craniocervical junction in brain dead patients. Our study showed that with a simple montage the nasopharyngeal electrode is an effective non-invasive monitor for brainstem activity and can be used as an early diagnostic indicator of brainstem death.     

Metastatic carcinoma to the cervical nodes from an unknown head and neck primary site: Is there a need for neck dissection?

BACKGROUND: The aim of the study was to evaluate the outcomes and patterns of failure in patients with metastatic carcinoma to cervical lymph nodes from an unknown head and neck primary origin, who were treated curatively with radiotherapy, with or without neck dissection. METHODS: The study included 61 patients referred to the McGill University Hospital Centers from 1987 to 2002. The median age was 57 years, with male to female ratio of 4:1. Distribution of patients by N status was as follows: N1, 16 patients (26%); N2a, 18 (30%); N2b, 13 (22%); N2c, 7 (11%); and N3, 7 (11%). Twenty patients underwent neck dissection (11 radical, 9 functional) and 41 patients had biopsy (9 fine-needle aspiration and 32 excisional biopsy). All patients received radiotherapy. The median dose to the involved node(s) was 64 Gy, and 60 Gy to the rest of the neck. Treatment of the neck was bilateral in 50 patients (82%) and ipsilateral in 11 (18%). The minimum duration of the follow-up was 12 months, with the median of 32 months. RESULTS: The 5- and 8-year overall survival for the whole population was 79% and 67%, respectively. There was no statistically significant difference in the 8-year actuarial overall survival (64.8% and 67.6%, respectively, p = .64) and local relapse-free survival (75% vs 74.5%, respectively, p = .57), among patients who had biopsy versus those who had neck dissection. CONCLUSION: In our experience, definitive radiotherapy to the neck and the potential mucosal sites, whether preceded by neck dissection or not, is effective to achieve a good local control rate in the unknown primary cancer of the head and neck. The indication for neck dissection, in particular for early nodal stage, is controversial.     

Ascending limb of the N20 component of somatosensory evoked potential--an analysis on direct recording from the human midbrain

Somatosensory evoked potential elicited by median nerve stimulation at the wrist was recorded from five loci on the trajectory of stereotactic rostral mensencephalic reticulotomy. Four distinct positive waves followed by one negative wave, the peak latency being 16.3 msec, were recorded from the rostral midbrain reticular formation near the medial lemniscus. The four positive waves were named as I, II, III, and IV respectively. Peak latency of these positive waves was 12.6, 13.7, 14.7 and 15.8 msec respectively. The first two positive waves (I, II) corresponded to P13 and P15 recorded over the scalp. The other two positive waves (III, IV) changed their polarity to negative at the level of the ventral thalamus and formed the ascending limb of N20 recorded over the scalp. N16 was most prominent at the level of nucleus ventrocaudalis externus. These findings suggest that the ascending limb of N20 is composed of at least three components, wave III, IV, and N16. The present report is compatible with the investigations by Abbruzzese et al.2) and Eisen et al.11) that there are several distinct dipoles between P15 and N20 of somatosensory evoked potential in man.     

Causes of family refusal for organ donation

Introduction

Family refusal represents a barrier for organ donation together with other cultural and religious factors possible ignorance and clinical obstacles.

Methods

We performed this retrospective study by phone employing our organ procurement unit database, using a list of families of potential organ donors who had refused organ donation.

Results

In 2009, 146 potential organ donor families refused donation. We contacted 81 families. The main reason expressed by there families to justify the refusal to donate the deceased's organs was denial and rejection of brain-death criteria (44.4%). Other causes were believing in a miracle (13.6%); fear about organ trade and unknown organ destination (9.9%); religious beliefs (8.6%); insecutrity about the brain-death diagnosis (6.2%); unstable family mood (6.2%); unknown donor wishes about donation (4.9%); belief in body integrity after death (3.7%); and fear of objection by other family members (2.5%).

Conclusion

Our findings showed several reasons for family refusal for organ donation; among the main cause is poor acceptance of brain death. It seems that increasing the knowledge of people about brain death and organizing strategies to confirm brain death for families are necessary to meet the organ shortage.     

Electrophysiological studies of human face perception. I: Potentials generated in occipitotemporal cortex by face and non-face stimuli.

This and the following two papers describe event-related potentials (ERPs) evoked by visual stimuli in 98 patients in whom electrodes were placed directly upon the cortical surface to monitor medically intractable seizures. Patients viewed pictures of faces, scrambled faces, letter-strings, number-strings, and animate and inanimate objects. This paper describes ERPs generated in striate and peristriate cortex, evoked by faces, and evoked by sinusoidal gratings, objects and letter-strings. Short-latency ERPs generated in striate and peristriate cortex were sensitive to elementary stimulus features such as luminance. Three types of face-specific ERPs were found: (i) a surface-negative potential with a peak latency of approximately 200 ms (N200) recorded from ventral occipitotemporal cortex, (ii) a lateral surface N200 recorded primarily from the middle temporal gyrus, and (iii) a late positive potential (P350) recorded from posterior ventral occipitotemporal, posterior lateral temporal and anterior ventral temporal cortex. Face-specific N200s were preceded by P150 and followed by P290 and N700 ERPs. N200 reflects initial face-specific processing, while P290, N700 and P350 reflect later face processing at or near N200 sites and in anterior ventral temporal cortex. Face-specific N200 amplitude was not significantly different in males and females, in the normal and abnormal hemisphere, or in the right and left hemisphere. However, cortical patches generating ventral face-specific N200s were larger in the right hemisphere. Other cortical patches in the same region of extrastriate cortex generated grating-sensitive N180s and object-specific or letter-string-specific N200s, suggesting that the human ventral object recognition system is segregated into functionally discrete regions.     

Pitfalls in cortical localization by intraoperative recording of cortical somatosensory evoked potentials]

Cortical somatosensory evoked potential (SEP) recordings were made in 11 patients who had lesions located in or near the somatosensory or motor gyri to localize the central sulcus and sensorimotor cortex during neurosurgical operations. Cortical localization was successful in 7 of the 11 patients by recording phase reversal waveforms of N20 and P20 at electrode sites in the hand area on opposite sides of the central sulcus. There were 4 cases in which the cortical localization failed. Locations of craniotomy were far distant from the central sulcus retrospectively in 2 of the 4 patients. Cortical SEPs couldn't be recorded despite probable exposure of the hand area and apparently adequate stimulation and recording conditions in 2 patients who had showed no or low amplitude scalp SEP preoperatively. In one of these 2 patients only low amplitude negative waves were recorded at the cortex which was thought far field potentials originated from subcortical structures. In 2 patients cortical SEP was monitored during the removal of the tumors and was useful to estimate the effects of the operative procedures on the sensorimotor cortex. It is concluded that the localization of cortical functions using cortical SEP is useful for reducing risk associated with intracranial surgery. However, we must be aware that there are some pitfalls in this method.     

Ventricular Dysfunction Associated With Brain Trauma Is Cause for Exclusion of Young Heart Donors

Objective

Ventricular dysfunction (VD) in the context of brain death (BD) is one medical cause that may be reversed to extend the range of donors for cardiac transplant programs. The aim of this study was to identify and quantify the causes for exclusion of potential heart donors and to define risk factors for VD among the BD population.

Materials and Methods

This study of 100 heart-beating potential donors defined subjects as those younger than 50 years. We defined hemodynamic dysfunction (HD) as failure to achieve hemodynamic objectives despite the use of inotropic agents by protocol or upon diagnosing VD.

Results

Among 246 BD subjects were 100 potential heart donors. Of these, 75 were transformed into real donors (RD) including 13 heart RD and 62 noncardiac RD. The conversion rate of BD subjects younger than 50 years to heart RD was 17%. When we analyzed the medical reasons for exclusion of the 62 donors who were not converted to heart RD, we observed that HD was the major cause (34%). When we analyzed the causes for exclusion related to cause of death, cranial trauma predominated (52%; P = .01; relative risk 3.5; 95% confidence interval 1.4-8.5).

Conclusion

Hemodynamic dysfunction represented the major cause for loss of heart donors; it was associated with younger patients with cranial trauma.     

The bispectral index, a useful adjunct for the timely diagnosis of brain death in the comatose trauma patient

Background

The bispectral index (BIS) is a processed electroencephalographic value (awake = 100, isoelectric = 0). The relationship of BIS and brain death (BD) is assessed.

Methods

BIS was evaluated in GCS 3 head-injured patients with BD (no brain function including apnea) or near BD (no apnea or negative ancillary test [cerebral perfusion and electroencephalogram]).

Results

In 27 patients, there were 37 BD evaluations (apnea assessment or ancillary test). BD was confirmed in 62% (n = 23). However, 38% (n = 14) showed near BD. BD BIS is 3 ± 5 and near BD BIS is 36 ± 31 (P = .002). In the 23 BD patients, BIS was <20 for 7 hours ± 6 hours before a BD evaluation was performed. Of 14 near BD evaluations, 9 (64%) had BIS ≥20. BIS <20 for predicting BD had a sensitivity of 100% (23/23), a positive predictive value of 84% (23/28), and a negative predictive value of 100% (9/9).

Conclusions

Distinguishing brain death and near brain death in severely comatose trauma patients is complex. By indicating the likelihood of brain death, BIS is an adjunct for efficient evaluation.     

Effects of discrimination difficulty on cognitive event-related brain potentials in patients with cochlear implants.

Cognitive event-related brain potentials (ERPs) recorded during a 2-tone discrimination (oddball) task were examined in 8 patients with cochlear implants. The aim of this study is to investigate the effects of discrimination difficulty formed by 4 conditions of stimulus contrast: the target stimuli were set at 2000, 1500, 1200, or 1100 Hz, and nontarget stimuli were set at 1000 Hz throughout. The averaged ERPs recorded after the target stimuli revealed N100, P200, N200, and P300 peaks, whereas those after the nontarget stimuli showed only N100 and P200 peaks. The peak latencies of the ERP components of early information processings (N100 and P200) were not significantly increased among the 4 conditions. In contrast, the latencies of late cognitive components (N2b and P300, whose peak latencies were longer than 250 msec) and reaction times were significantly increased as target discriminability decreased. In conclusion, early information processings were not delayed by the discrimination difficulty, but cognitive processings were delayed in patients with cochlear implants. Because the N2b amplitude, which is considered to be associated with controlled processings, was much larger than that previously reported from subjects with normal hearing, it is suggested that patients with cochlear implants make a considerable effort to process their poor auditory information.     

Attitudes of Medical Students About Brain Death and Organ Donation

Introduction

There have been publications on the attitudes of the general Iranian population and health care personnel about brain death and organ donation; however, there is little information about such attitudes of medical students. In 2006, a survey was conducted in Tehran about the attitudes of medical students in a hospital with a transplantation program.

Material and Methods

The general population, health care personnel, and medical students were surveyed, and data were extracted from interviews with 41 medical students. The survey included 35 items about attitudes toward brain death and organ transplantation.

Results

Nine students (22.0%) had ever seen a transplant recipient, and 7 (17.1%) had ever seen a brain-dead patient. Thirty-four students (82.9%) agreed with organ donation after brain death. Six students (14.6%) had received information through university lectures, and 40 (97.5%) perceived a need for further information about organ donation and brain death in the university curriculum. Nine students (22.0%) had an organ donor card.

Conclusion

Most Iranian medical students have neither been exposed to brain death or organ recipients nor received appropriate information about organ donation and transplantation.     

Effects of ketamine on somatosensory evoked potentials during nitrous oxide anesthesia in humans

The effects of ketamine with 60% nitrous oxide were studied on subcortical sensory evoked potentials recorded at Erb's point (N9), neck (N13) and on cortical potentials recorded at the scalp (N20) following median nerve stimulations in 7 neurologically normal patients. Latencies and amplitudes of the potentials were measured and compared with postinduction control values taken during inhalation of 60% nitrous oxide. Ketamine 2 mg.kg-1 (iv) was administered initially and incremental dose was 50 micrograms.kg-1.min-1. N20 latency decreased at 15, 30 minutes after ketamine administration from a control value of 18.7 +/- 0.9 msec to 18.2 +/- 1.1, 18.2 +/- 1.1 msec respectively, and N13-N20 interpeak latency decreased from 6.0 +/- 0.4 msec to 5.5 +/- 0.7, 5.4 +/- 0.7 msec (mean +/- SD). The author concluded that during nitrous oxide-based anesthesia, ketamine did not inhibit specific thalamoneocortical pathways.