Referred pain from intraneural stimulation of muscle fascicles in the median nerve

Microelectrode recordings were obtained from 118 cutaneous and 26 muscle fascicles in the intact median nerves of healthy human subjects. The exploring electrodes were also used for painful electrical stimulation of the identified fascicles. Cutaneous pain was accurately projected to fields within the median innervation territory. Deep pain was projected to muscles innervated by the median nerve, but in 7 experiments it was also segmentally referred to muscles in the ipsilateral upper arm, axilla or chest. Reaction time measurements indicated that referred pain was conveyed by afferent group III fibres from muscle, but did not exclude a possible contribution by group IV fibres. Referred pain was influenced by temporal and spatial summation of the afferent inflow. The magnitude of referred pain was positively correlated to the stimulation frequency of deep nociceptive fibres. The results from this study on experimentally induced pain confirm clinical observations of proximal referral of pain in patients with median nerve entrapment, and prompt consideration of possible involvement of nerve fascicles supplying deep structures in the forearm or hand in the differential diagnosis of pain in the chest and upper arm.     

Neurophysiologic findings in early acute inflammatory demyelinating polyradiculoneuropathy.

BACKGROUND: Patients with early acute inflammatory demyelinating polyradiculoneuropathy (AIDP) may not meet the current neurophysiologic criteria. OBJECTIVE: To document neurophysiologic findings in early AIDP. METHODS: Clinical and neurophysiologic data from 38 AIDP patients, assessed within 10 days of symptom onset were reviewed. RESULTS: In addition to absent H reflexes and abnormal F-wave responses in the acute stage of AIDP, abnormalities of blink reflexes, upper limb sensory responses abnormalities with spared sural responses, presence of distal CMAP dispersion, and A-waves were frequently observed. Established demyelinating neurophysiologic parameters were infrequently seen. CONCLUSIONS: Abnormalities of H reflexes and F responses were most frequently noted in early AIDP. Additionally, distal temporal dispersion, prolonged or absent blink reflexes, and A-waves were often present in the acute stage of AIDP when classic diagnostic criteria of AIDP were not satisfied. SIGNIFICANCE: Neurophysiologic studies in early AIDP frequently reveal abnormalities that are not specific of primary demyelinating neuropathy.     

Transcutaneous electrical nerve stimulation: A microneurographic and perceptual study

With the aim of studying peripheral physiological mechanisms involved in transcutaneous electrical nerve stimulation (TENS) for the suppression of pain, the authors have examined 14 healthy volunteers in the perceptual part and 8 in the microneurographic part of this study. For pain suppressing stimulation they have used ring electrodes and stimulators capable of producing rectangular, sine wave, triangular and hybrid wave forms. Pain was induced with electrical stimuli on the distal phalanx of the middle finger.TENS with rectangular, sine wave and triangular pulses activates mainly Aβ, but also some Aδ fibres. Pain suppressing capacity of different wave forms used was the same and was achieved with stimuli close to the threshold for pain. Pain was most effectively dimished when noxious and pain suppressing stimuli were applied to the same finger; this effect was smaller with the two stimuli on neighbouring fingers and very weak when pain suppressing stimulus was applied to the contralateral hand. Increases in stimulus frequency resulted in an increased and variable latency as well as intermittent blocking of those spike components which had been near threshold at low frequency stimulation. This is interpreted as being due to local changes in excitation threshold. In surface-recorded averaged electroneurograms this effect was seen as amplitude decrement and increased response duration, but was not due to impulse transmission failure in Aδ fibres as seen microneurographically. On continuous high frequency stimulation, the intensity of sensation elicited diminished, although there was no change in the microneurogram.The authors conclude that the peripheral contribution to the analgesic effects of TENS seems to be unimportant.     

Analysis of peripheral nerve function in streptozotocin diabetic rats

Conduction velocity of rat sciatic nerve, estimated both in vivo and in vitro, did not change during 2–21 weeks following induction of diabetes by injection of streptozotocin. During this period blood sugars were in the range 17.6–30.4 mM and symptoms of uncontrolled diabetes were noted. The failure of velocity to decrease contrasts strongly with several previous reports, while the failure to increase with age may be explained with the aid of published morphometric data.Experiments on nerve fibres isolated from streptozotocin-diabetic rats confirmed that the nerve function was normal in respect of action and resting potential. Potential clamp analysis of nodal membrane similarly indicated that these fibres had normal permeability properties.     

The subthalamic nucleus in Parkinson’s disease: power spectral density analysis of neural intraoperative signals

Abstract. To test a new tool for the neurophysiological identification of the human subthalamic nucleus (STN) during stereotactic surgery for the implantation of deep-brain-stimulation (DBS) electrodes, we analysed off-line the intraoperative signals recorded from patients with Parkinsons disease. We estimated the power spectral density (PSD) along each penetration track (8 patients, 13 sides) and determined the spatial correlation of the PSD with the target location estimated from neuroimaging procedures (anatomical target), and with the final target location derived from standard intraoperative neurophysiological procedures for STN localization (clinical target). At each step we recorded the on-line signal for 120 seconds; because the PSD was estimated by calculating the periodogram for 6-second epochs of neural signal, we had 20 epochs at each step. When the electrode track crossed the STN, the PSD in the 0.25-2.5 kHz band increased, peaking on average <0.5 mm cranial to the clinical target and 1.00±1.51 mm caudal to the anatomical target. When the track was outside the nucleus, the PSD remained unchanged. Even on recordings with low signal-tonoise ratio, off-line PSD analysis of neural signals showed a good correspondence with the target indicated by the surgical team. On-line intraoperative estimation of the PSD may be a simple, reliable, rapid and complementary approach to electrophysiological monitoring during STN surgery for Parkinsons disease.* The first two authors are in alphabetical order because they contributed equally to this work.     

Neurons with radial basis like rate functions

Artificial neural networks constructed with "locally tuned processing units" and more generally referred to as "radial basis function networks" have been proposed by a number of workers. In this communication, I submit a conjecture, based on indirect experimental and direct computational evidence of the Hodgkin-Huxley model, that there may be biological neurons in nervous systems for which the rate function is locally tuned. If proved to be valid, this conjecture may simplify neurodynamic models of some functions of nervous systems.     

大脑半球切除术后远期体感诱发电位成分中N18神经发生源的相关研究

目的探讨人类体感诱发电位(SEP)中N18的确切神经发生源.方法分别对20例大脑半球切除术后远期的病例和12例正常人进行正中神经(MN)刺激的SEP.在SEP中,采用头参考点与非头参考点记录的方法.同时,所有病例进行MRI检查.结果所有20例大脑半球切除术后远期的病例,皮质下至脑干中段发生广泛萎缩.手术侧未引出N20,但P14的波峰潜伏期(LP)为12.5 ms±0.8 ms,而N18的LP为17.6 ms±1.6 ms,均在正常范围.结论 N18的确切神经发生源应在延髓节段.     

脉·经脉·经络——细筋·系·神经 经络概念的内涵演化与神经的联系

经络学说起源于对“脉”的解剖生理学认识 ,以脉行的路径为经脉 ,以脉行的分支横出的径路为络脉 ,从而逐渐形成了经脉和络脉的概念。对经络学说提出挑战的是来自西方医学的传入 ,即人们在认识神经学说的结构与功能之后 ,来阐释经络沟通人体体表与体表上、下之间 ,体表与内脏内、外之间特异联络、调控和反应功能。在明末传入的西方解剖生理学 ,或是在晚清西方医学科学的东传过程中 ,与经络功能相关的中医词汇如“细筋”“系”等曾作为“nerve”的汉译名词 ,从而在中西医汇通的初创阶段 ,奠定了经络与神经功能活动相关的文字转换基础     

Neurophysiology of penile erection

Summary In 6 dogs and 6 monkeys electrical stimulation of the cavernous, pudendal and hypogastric nerve was performed to gain better understanding of the erectile neurophysiology. Arterial flow, intracorporeal pressure and venous restriction studies during single and combined neurostimulation demonstrated that initiation and maintenance of erection is a parasympathetic phenomenon. Penile rigidity however, could only be achieved with additional pudendal nerve stimulation resulting in muscular compression of the blood distended cavernous bodies. Detumescence or subsidence of erection is primarily under sympathetic control, due to inhibition of sinusoidal smooth muscle relaxation. On the basis of our observations we conclude that penile erection is dependent upon three neurophysiological mechanisms: 1. the parasympathetic vascular mechanism, the somatomotor muscular mechanism and the sympathetic inhibitory mechanism.Part of this paper was presented at the 9th Symposium of the Association for Experimental Urology of the German Urological society, June 17–18, 1988, Aachen, Federal Republic of Germany     

Maturation of evoked mossy fiber input to rat cerebellar Purkinje cells (II)

Summary The aim of this work was to establish a time sequence for the functional maturation of the mossy fiber afferent system to the cerebellum, in order to place it in the context of overall cerebellar cortical development. Rat pups at various ages were anesthetized with 0.5% halothane, and Purkinje cell activity was monitored extracellularly as limbs were electrically stimulated. The results showed that Purkinje cells can receive input from the periphery via the mossy fiber system at least by the seventh postnatal day, which is relatively early in overall cerebellar development. It is clear that synaptic transmission begins soon after the mossy fiber terminals and granule cell dendrites are in physical proximity. Initially, such input has a long latency (66 msec), is easily fatigued (at 10/sec), and has a prolonged duration of excitatory effect on Purkinje cells (27 msec). These and other functional parameters become mature by the third postnatal week (6–9 msec latency, following frequency above 20/sec), which is well before overall cerebellar cortical cytological development is completed. The maturation of many functional parameters of the cerebellar afferent systems and the acquisition of new motor behaviors are shown to emerge in parallel. Motor function appears to correlate with the establishment of a mature time scale of operation of the cerebellar circuitry.Supported by N. I. H. Grant 5-R01-GM00133 and N.S.F. Grant GB 43301