Differences in perception and brain activation following stimulation by large versus small area cutaneous surface electrodes.

INTRODUCTION: Application of electrical stimulation through conventional surface electrodes activates both non-nociceptive and nociceptive fibres. To encompass this problem, electrical stimulation through small area pin electrode was introduced where subjective description of stimulation quality indicated preferential activation of nociceptors. The present study aimed to show that brain areas involved in nociceptive processing are activated by stimulation through cutaneous pin electrode (CPE) to a larger extent than conventional surface electrodes. METHODS: Evoked potentials (EPs) were induced by electrical stimulation through conventional surface and CPE electrodes. The EPs were recorded from 62 scalp electrodes in 12 healthy volunteers where stimulation intensity was 10 times the sensory threshold. Dipolar models of brain sources were built by using the brain electrical source analysis. RESULTS: The solution for the conventional large area surface electrode was a four-dipole model including contralateral primary somatosensory cortex, bilateral secondary somatosensory cortex (SII) and mid-cingulate sources. The solution for CPE was a five-dipole model and very similar to that previously described to explain the topography of laser EPs. The solution included bilateral SII, bilateral insula and mid-cingulate sources. Since laser stimuli mainly activate nociceptive fibres, the strong similarity suggests that mainly nociceptive inputs are involved in generation of CPE-evoked responses. CONCLUSION: The current study gives evidence that CPE activates the nociceptive brain areas to a greater extent than conventional surface electrode. Therefore, CPE should preferentially be utilized in future studies where electrical stimuli are used to study nociception.

The effects of training time, sensory loss and pain on human motor learning.

This study determined, in humans, the effects of (i) the number of within-session task repetitions (72 or 144 over a period of 15 or 30 min, respectively) on the time course of motor learning in a long-term (seven consecutive daily motor-training sessions and a 1-week post-follow-up) novel tongue-task training regime and (ii) somatosensory manipulations (capsaicin-induced intra-oral pain or lidocaine-induced sensory loss of the tongue tip) on motor learning in a short-term (single motor-training session consisting of 72 within-session task repetitions over a period of 15 min) novel tongue-task training regime. Novel tongue-task training consisted of tracking a moving target box by generating a pre-set amount of tongue-protrusion force onto a force lever. Analysis of motor behaviour revealed (i) a higher within-session gain for the 30-min tongue-task training regime, but this difference did not differentially affect the time course of the overall motor performance or additional motor performance variables between the 15- and 30-min tongue-task training regimes in subsequent training sessions. (ii) somatosensory manipulations of the tongue tip reduced the gains in overall motor performance, and this reduced motor performance was mainly characterized by exaggerated undershoot errors and delayed reaction times for the lidocaine tongue-task training regime and exaggerated overshoot and undershoot errors as well as delayed reaction times for the capsaicin tongue-task training regime. It is concluded that extended within-session task repetitions do not facilitate additional long-term gains in overall motor performance and intra-oral sensory loss or pain hinders motor learning.

Experimental validation of the nerve conduction velocity selective recording technique using a multi-contact cuff electrode.

The earthworm (Lumbricus terrestris) is presented as an in vitro model of a peripheral nerve containing only two fibers each with distinctly different conduction velocities, the median and lateral giant fibers (MGF and LGF). The worm model is used with a multi-contact cuff electrode to validate the spatial-temporal filtering effect of different electrode contact configurations and the effect of applying a delay adder and matched filter tuned to either the MGF or LGF action potential (AP) to extract conduction direction and velocity from the recording. The results confirmed the known effect of inter-electrode spacing and bipolar and tripolar recording configuration on the AP amplitude. It also demonstrates a crossover point where the amplitude of the tripolar recording is larger than the monopolar recording, an effect of the slower action potential conduction velocities in the worm. The delay adder was found to be an effective velocity sensitive filter, able to discriminate units based on conduction velocity. The matched filter to be an effective means to eliminate artifact and increase signal to noise ratios, however was not found to improve selectivity.

Selective activation of small-diameter motor fibres using exponentially rising waveforms: a theoretical study.

The present study investigated the possibility of using exponentially rising waveforms for selectively activating small motor fibres in a nerve bundle enclosed by a cuff electrode. Exponentially rising waveforms were studied using models of motor fibres and a volume conductor model. With an exponentially rising waveform (duration: 2 ms, time constant: 1 ms) large (15.5 microm) and small (8 microm) nerve fibres located at the edge of the nerve bundle had a current threshold of 125 microA and 53 microA, respectively. These reversals in the recruitment order of large and small nerve fibres located at the edge of the nerve bundle were observed for exponentially rising waveforms of 2, 4, and 6 ms in duration with time constants of 0.9, 0.6 and 0.6 ms, respectively. Reversals of the same nerve fibres located at the centre of the nerve bundle were observed for exponentially rising waveforms of 4 and 6 ms in duration, with a time constant of 0.6 ms for both waveforms. The underlying mechanism for selective activation of small nerve fibres with exponentially rising waveforms was found to be a combination of a decrease in the size of the local excitations in the centre node due to sodium channel inactivation and blocking of action potentials in large nerve fibres due to their larger difference in the membrane potential of adjacent nodes. The exponentially rising waveforms were compared with both rectangular prepulses and ramp prepulses. The rectangular prepulses were found to be unable selectively to activate small nerve fibres with the volume conductor model and criteria used in the present study, whereas the ramp prepulses performed as well as the exponentially rising waveforms. In conclusion, a novel stimulation paradigm has been proposed that may provide smooth, gradual control of muscle force with minimum fatigue.

Metastatic tumors to the parotid and submandibular glands--analysis and differential diagnosis of 108 cases.

The distinction between primary salivary gland tumors and metastases of other primary tumors in salivary glands is of special importance for therapy and prognosis. In the files of the Salivary Gland Register, 10,944 cases were collected during 1965 and 1985. Among these cases, there were 108 cases of metastatic tumors to the parotid and submandibular gland. The pathohistological analysis of these tumors revealed the following data: 47 cases (43%) of metastatic tumors were localized in the parenchyma of the parotid gland (37 cases) or of the submandibular gland (10 cases). 61 cases (57%) displayed metastases in the lymph nodes of the parotid gland (38 cases) or of the submandibular gland (23 cases). The sublingual gland was free of metastatic tumors. 65 metastatic tumors originated from primary tumors in the neighborhood (head and neck). 32 tumors were carcinomas of the skin, 17 tumors were melanomas, and 13 tumors were nasopharyngeal cancers. Metastases of thyroid cancers were found in 3 cases. The relative frequency of metastases in the lymph nodes of the salivary glands is due to the intense drainage with lymph vessels and the presence of many lymph nodes which are localized especially in the gland parenchyma or around the parotid gland. 21 metastatic tumors originated from primary tumors distant from the head and neck region. There were metastases of lung cancers (7 cases), renal cancers (6 cases), mammary cancers (6 cases), colonic cancer (1 case) and uterus cancer (1 case). Clear cell carcinomas in salivary gland tissue should always be checked for a metastasis of a primary renal cancer.(ABSTRACT TRUNCATED AT 250 WORDS)