Stimulation Of Different Sites Research Articles

Electrically Evoked Auditory Brainstem Response Using Extracochlear Stimulation at Different Cochlear Sites: A Comparison With Intracochlear Stimulation.

The distribution and extent of excitable spiral ganglion neurons (SGNs) have been investigated using the electrically evoked auditory brainstem response (EABR) during preoperative and perioperative periods. In this study, we investigated the EABR with extracochlear stimulation (eEABR) as a preoperative test to estimate these factors. Sixteen male Sprague-Dawley rats were used in this study. Experiments were conducted in nine rats with normal hearing and seven rats that were partially deafened with ouabain treatment. Each experiment involved the following steps: extracochlear stimulating electrode placement at three different sites along the axis of the cochlea and eEABR recordings; cochleostomy and four-channel intracochlear array implantation, followed by EABR recordings with various electrode pair combinations; and after electrophysiological measurements, harvest of the cochleae for histopathological evaluation. The slope characteristics of the amplitude growth function measured from eEABR and EABR, frequency-specific auditory thresholds, and the density of SGNs were compared. Similar trends were observed in slope changes on different sites of stimulation with both types of stimulation in normal-hearing animals-specifically, a monotonically increasing slope with increasing distance between bipolar pairs. In addition, eEABR slopes showed significant correlations with EABR slopes when the expected cochlear regions of stimulation were similar in normal-hearing animals. In partially deaf animals, the auditory thresholds at several frequencies had a significant correlation with the eEABR slopes of each extracochlear electrode at the apical, middle, and basal cochlear positions. This indicated that increasing the regions of cochlear stimulation had a differential impact on eEABR slopes, depending on the neural conditions. Our results indicated that eEABR slopes showed significant spatial correlations with the functionality of the auditory nerve. Therefore, eEABR tests at various cochlear positions might be used for estimating the extent of excitable SGNs in cochlear implant candidates prior to implantation.

Abnormal Circadian Modification of Aδ-Fiber Pathway Excitability in Idiopathic Restless Legs Syndrome.

Restless legs syndrome (RLS) is characterized by unpleasant sensations generally localized to legs, associated with an urge to move. A likely pathogenetic mechanism is a central dopaminergic dysfunction. The exact role of pain system is unclear. The purpose of the study was to investigate the nociceptive pathways in idiopathic RLS patients. We enrolled 11 patients (mean age 53.2 ± 19.7 years; 7 men) suffering from severe, primary RLS. We recorded scalp laser-evoked potentials (LEPs) to stimulation of different sites (hands and feet) and during two different time conditions (daytime and nighttime). Finally, we compared the results with a matched control group of healthy subjects. The Aδ responses obtained from patients did not differ from those recorded from control subjects. However, the N1 and the N2-P2 amplitudes' night/day ratios after foot stimulation were increased in patients, as compared to controls (N1: patients: 133.91 ± 50.42%; controls: 83.74 ± 34.45%; p = 0.016; Aδ-N2-P2: patients: 119.15 ± 15.56%; controls: 88.42 ± 23.41%; p = 0.003). These results suggest that RLS patients present circadian modifications in the pain system, which are not present in healthy controls. Both sensory-discriminative and affective-emotional components of pain experience show parallel changes. This study confirms the structural integrity of Aδ nociceptive system in idiopathic RLS, but it also suggests that RLS patients present circadian modifications in the pain system. These findings could potentially help clinicians and contribute to identify new therapeutic approaches.

P108 Remediation of cognitive impairment due to sleep deprivation: A rTMS pilot study

Introduction The lack of sleep is associated with diminished cognitive performance. rTMS has been applied in sleep deprived subjects, showing a decrease in response times (upper middle occipital gyrus); but this effect is no longer found after recovery ( Luber et al., 2008 ). Objectives To explore the effects of high frequency stimulation in different areas. Patients & methods 6 healthy right-handed subjects were randomly assigned to one stimulation group: medial frontal gyrus, medial occipital gyrus or SHAM. Subjects completed one initial fMRI session and another final session (post 24 h sleep deprivation & stimulation). Letters were presented for 500 ms in 5 min blocks (300 letters & 60 targets). Stimulation consisted of a 20-min session at 5 Hz in the left hemisphere at 100% of the MT. Mood (VAS) and sensation (1:10) were measured. For 1-back, accuracy increased for MFG (3.33%) and for 2-back increased in MOG (25%). MOG group showed shorter response times in 1-back (5.05%) and 2-back (18.32%). Sensation scale measure was 3(±1.9), subjects were not able to distinguish whether it was true or false stimulation. VAS results are shown in Fig. 1 Download : Download high-res image (455KB) Download : Download full-size image (0: minimum value and 10: maximum value). MFG group: activation increased was found for both contrasts (1 & 2-back) especially in areas related to frontal lobes. MOG group: activation decreased in frontal lobes (1-back). SHAM group: increment at parietal lobe, prefrontal cortex, cingulate gyrus and temporal lobe for both contrasts (Fig. 2 Download : Download high-res image (618KB) Download : Download full-size image ). Conclusion Stimulation has a positive effect in the perception of symptoms related to SD. In MOG group, subjects showed better accuracy and response times. These findings may be caused by the stimulation of parietal-temporal-occipital association area (in charge of focusing specific objects and rejecting others, attention in spatial loctralization and plays an important role in verbal memory); located near MOG ( Rhoades, 2009 ). Results indicate that there are differences between the different sites of stimulation, so it will be interesting to further explore these areas with a larger size population.

Sural sensory nerve action potential: A study in healthy Indian subjects.

Background:The sural sensory nerve action potential (SNAP) is an important electrodiagnostic study for suspected peripheral neuropathies. Incorrect technique and unavailability of reference data can lead to erroneous conclusions.Objectives:To establish reference data for sural SNAP in age-stratified healthy subjects at three sites of stimulation.Materials and Methods:A prospective study was conducted in 146 nerves from healthy subjects aged between 18 years and 90 years, stratified into six age groups (a = 18-30 years, b = 31–40 years, c = 41–50 years, d = 51–60 years, e = 61–70 years, and f >71 years). Sural SNAP was recorded antidromically, stimulating at three sites at distances of 14 cm, 12 cm, and 10 cm from the recording electrode. Mean – 2 standard deviation (SD) of the transformed data was used to generate reference values for amplitudes. Analysis of variance (ANOVA) test was used for inter-group and between three sites comparisons of amplitudes.Results:The lower limits of amplitude at 14 cm were 12.4 μV, 10.4 μV, 6.5 μV, 5.3 μV, 2.9 μV, and 1.9 μV; at 12 cm were 13.5 μV, 13.6 μV, 8.5 μV, 7.8 μV, 3.5 μV, and 2.8 μV; and at 10 cm were 16.3 μV, 16.3 μV, 11.1 μV, 10.0 μV, 4.8 μV, and 3.7 μV for groups a, b, c, d, e, and f, respectively. A statistically significant difference in amplitudes was noted from the three different sites of stimulation (P < 0.001). The amplitude differed significantly above the age of 60 years (P < 0.01) but not between groups e and f (P > 0.05).Conclusion:This study provides reference data for sural SNAP in Indian population at three different sites of stimulation along the calf in six age groups. It also shows significant variation in amplitude from the three different sites of stimulation.

Screening and Optimization of Nerve Targets and Parameters Reveals Inhibitory Effect of Pudendal Stimulation on Rat Bladder Hypersensitivity.

Neuromodulation has been reported to reliably improve symptoms of bladder overactivity and sometimes pain. The effect of electrical stimulation of several nerve pathways demonstrated to alter cystometric responses to bladder distension was examined on nociceptive responses in models of bladder hypersensitivity. Bladder hypersensitivity was produced by several published methods including neonatal inflammation, acute inflammation, and chronic stress. Effects of different sites of stimulation (L6 and T13 nerve roots, proximal and distal pudendal nerves [PNs]) on nociceptive reflex responses to urinary bladder distension in urethane-anesthetized female rats were assessed and a parametric analysis of parameters of stimulation was performed. Bilateral biphasic stimulation of the proximal PNs resulted in statistically significant inhibition of visceromotor and cardiovascular responses to bladder distension in rats made hypersensitive by neonatal bladder inflammation. We found a range of optimal stimulation frequencies (5-10 Hz) which produced robust inhibitory effects when using short pulse widths (100-240 μs). Onset of inhibition was within minutes and persisted for several minutes after the stimulus was discontinued. Use of bilateral PN stimulation in acute inflammation and stress-induced hypersensitivity models as well as unilateral stimulation, very distal PN cutaneous branch stimulation, and stimulation of the T13 and L6 nerve roots all proved ineffective with the parameters used. This study suggests that inhibitory effects of bilateral PN stimulation can be evoked in a rodent hypersensitivity model at relatively low frequencies with short pulse widths. The onset of effect is rapid, which suggests the potential for treating episodic pain in painful bladder disorders.

Modulation of Perception or Emotion? A Scoping Review of Tinnitus Neuromodulation Using Transcranial Direct Current Stimulation

Background. Tinnitus is the phantom perception of sound and can have negative effect on the quality of life. Transcranial direct current stimulation (tDCS) is a noninvasive neuromodulation technique, which can increase or decrease the cortical excitability in the brain region to which it is applied. tDCS has been used for tinnitus research since 2006. Objective. To investigate whether tDCS affects tinnitus perception, related emotion, or both, and the potential implications for tinnitus management. Methods. A scoping review was undertaken using the methods proposed by Arksey and O’Malley. After initial consideration of title relevance and reading abstracts, 15 studies were included in this review. The data from these studies were charted to investigate the impact of tDCS on tinnitus perception and emotions. Results. tDCS results in transient suppression of tinnitus loudness and annoyance; however, it does not lead to long-term impact on tinnitus related emotion. Local stimulation of different sites of stimulation (left temporoparietal area, dorsolateral prefrontal cortex, and auditory cortex) might modulate tinnitus perception (loudness) and emotions differently; however, further research is needed to explore this hypothesis. This review has identified aspects of methodologies that require attention in upcoming tinnitus and tDCS trials to offer better insights. Conclusions. tDCS is an effective research tool for transient tinnitus neuromodulation. However, efforts should be invested in designing clinical trials using local and multiple sites of stimulation, optimized parameters, and objective outcome measures before it can be translated in to a clinical tool for tinnitus management.

Recall of spatial patterns stored in a hippocampal slice by long-term potentiation

Nervous systems are thought to encode information as patterns of electrical activity distributed sparsely through networks of neurons. These networks then process information by transforming one pattern of electrical activity into another. To store information as a pattern, a neural network must strengthen synapses between designated neurons so that activation of some of these neurons corresponding to some features of an object can spread to activate the larger group representing the complete object. This operation of pattern completion endows a neural network with autoassociative memory. Pattern completion by neural networks has been modeled extensively with computers and invoked in behavioral studies, but experiments have yet to demonstrate pattern completion in an intact neural circuit. In the present study, imaging with voltage-sensitive dye in the CA3 region of a hippocampal slice revealed different spatial patterns of activity elicited by electrical stimulation of different sites. Stimulation of two separate sites individually, or both sites simultaneously, evoked "partial" or "complete" patterns, respectively. A complete pattern was then stored by applying theta burst stimulation to both sites simultaneously to induce long-term potentiation (LTP) of synapses between CA3 pyramidal cells. Subsequent stimulation of only one site then activated an extended pattern. Quantitative comparisons between response maps showed that the post-LTP single-site patterns more closely resembled the complete dual-site pattern. Thus, LTP induction enabled the CA3 region to complete a dual-site pattern upon stimulation of only one site. This experiment demonstrated that LTP induction can store information in the CA3 region of the hippocampus for subsequent retrieval.

Individual auditory thalamic reticular neurons have large and cross-modal sources of cortical and thalamic inputs

In the present study, the sources of thalamic and cortical inputs of thalamic reticular nucleus (TRN) neurons were examined by investigating the responses of the TRN neurons to electrical stimulation of different sites in the thalamus and the cortex of the rat. The recurrent excitation of the corticothalamic system that is triggered by electrical stimulation was eliminated by ablating the auditory cortex and by temporarily inactivating the medial geniculate body (MGB), when studying the sources of thalamic and cortical inputs, respectively. Single TRN neurons responded to electrical stimulation of 50-100 μA of the thalamus over a large area (dorsoventrally 1.2-2.4 mm and mediolaterally 1.0-2.3 mm, n=9). Four of 16 auditory TRN neurons responded to electrical stimulation of the lateral geniculate nucleus. The TRN neurons responded to cortical stimulation over a rostrocaudal distance of 2.6±0.5 mm (range: 1.5-3.5 mm, n=24) of the auditory cortex. Visual or auditory TRN neurons also responded to electrical stimulation in the auditory or visual cortices, respectively. The present study revealed that each TRN neuron received a wide range of inputs from both ascending thalamic and descending cortical projections. The projection could be cross-modal. Having a strong and lasting inhibition on the thalamus, the TRN neurons are likely to be involved in adjusting global states relating to awareness and attention in the thalamocortical system.

Site-specific differences in central processing of visceral stimuli from the rectum and the descending colon in men

It has been reported that different brain activation areas are demonstrated during somatosensory and visceral stimulation. However, no study thus far has investigated how activated patterns in the human brain differ during visceral stimulation of different sites of the digestive tracts. The aim of this study was to determine possible site-specific differences in brain responses and perceptions during visceral stimulation of two different sites, the intraluminal distentions of the rectum and descending colon. Regional cerebral blood flow was assessed in 32 healthy right-handed male subjects using H(2)(15)O positron emission tomography during distention of the rectum (R group, n = 16) or descending colon (DC group, n = 16) at 40 or 20 mmHg. R group reported significantly higher scores of abdominal pain (P < 0.05) and urge to defecate (P < 0.001) during the application of stimulus at 40 mmHg compared with DC group but not of abdominal bloating or anxiety. In comparisons of response to the 40-mmHg stimulus, R group showed significantly greater activation in posterior midcingulate cortex (MCC) and right anterior and posterior insula, whereas DC group showed greater activation in subgenual anterior cingulate cortex (ACC), perigenual ACC and left orbitofrontal and superior temporal cortices. These findings suggest that central projections of painful visceral stimulation from the rectum and descending colon differ in affective, cognitive and nociceptive processing in the brain, which may result in different perceptions of visceral stimulation from different sites.

Sham transcranial magnetic stimulation using electrical stimulation of the scalp

BACKGROUND: Most methods of sham, repetitive transcranial magnetic stimulation (rTMS) fail to replicate the look, sound, and feel of active stimulation in the absence of a significant magnetic field. OBJECTIVE/HYPOTHESIS: To develop and validate a new method of sham rTMS appropriate for a double-blind, placebo-controlled study with subject crossover. METHODS: The look and sound of active rTMS was replicated using a matched, air-cooled sham TMS coil. Scalp muscle stimulation associated with rTMS was replicated using large rubber electrodes placed over selected muscles. The intensity and pulse width of electrical stimulation necessary to match 1-Hz rTMS was developed in one sample of normal subjects. The sham technique was validated in back-to-back comparisons with active rTMS in new samples of normal subjects who were either naïve or experienced with rTMS. RESULTS: Subjects naïve to TMS could not tell which type of stimulation was active or sham or which was electrical or magnetic. Naïve subjects incorrectly picked sham stimulation as active, when forced to choose, because electrical stimulation felt more focused than magnetic stimulation. Subjects experienced with TMS could correctly identify sham and active stimulation. Experimenters could detect subtle differences between conditions. CONCLUSIONS: This method of sham rTMS closely mimics the look, sound, and feel of active stimulation at 1Hz without creating a significant magnetic field. It is valid for use with naïve subjects and in crossover studies. It can accommodate differences in scalp muscle recruitment at different sites of stimulation, and it could potentially be used with higher frequency stimulation.

Axonal excitability in the forearm: Normal data and differences along the median nerve

Objective This study was designed to validate excitability studies of motor axons in the median nerve at the elbow, innervating forearm muscles (flexor carpi radialis, FCR) and collect normal data for this stimulation site. The differences in measures of excitability due to different sites of stimulation or a different test muscle group was also determined. Methods The median nerve was stimulated at the elbow and excitability studies were recorded from FCR and abductor policis brevis, APB. Further studies stimulated the median nerve at the wrist and recorded from APB. The study was performed using the TRONDCM protocol of QTRACS. Results Stimulus-response curves for FCR were significantly less steep than those for APB. There was “fanning in” of threshold electrotonus and less accommodation to hyperpolarising pulses for FCR axons. FCR studies showed significantly less supernormality. Conclusion There are differences in axonal excitability along a single nerve in the human upper limb, even when the nerve is stimulated at one site and recordings are made from different muscles. Significance Normal values for one muscle group cannot be assumed to be the same for a different muscle group. The findings for FCR axons will be of value in studies on patients with central nervous system disorders.

The topography of activity transmission between lateral entorhinal cortex and subfield CA1 of the hippocampus

It is important to establish how information is transmitted through the hippocampal formation because of the structure's critical role in memory and spatial processing. Here we provide evidence that challenges the hypothesis that information is processed in parallel closed entorhinal-CA1 loops. We tested the hypothesis by mapping, throughout hippocampal subfield CA1, field potentials evoked by stimulation of different sites in lateral entorhinal cortex in awake rats, thereby establishing the topography of electrophysiological transmission between the entorhinal cortex and CA1. The results established that antidromic and orthodromic responses evoked from the same entorhinal site occurred in spatially separated CA1 areas, with antidromic responses being located more septally than orthodromic responses. Thus, an entorhinal site receives information from a CA1 area located closer to the septal pole of the hippocampus and transmits it to the next CA1 area located closer to the temporal pole. Accordingly, processing in the hippocampal formation is by open rather than closed loops. Activation occurred first in CA1 close to its septal pole and spread towards its temporal pole. Four successively activated CA1 areas, oriented at an angle to the longitudinal axis of the hippocampus, were distinguished. Overall, the findings indicate that information can potentially be transmitted from the septal to the temporal end of the hippocampal formation via an ordered succession of hippocampal and entorhinal areas that form a three-dimensional spiral pathway.

Medium- and long-term survival after pacemaker implant: Improved survival with right ventricular outflow tract pacing

Long-term prognosis after pacemaker implant depends on numerous variables, particularly structural heart disease. There is evidence that apical stimulation could favor the development of heart failure and, therefore, influence mortality. Other right ventricular pacing sites have been studied, for example the outflow tract, but no reports regarding long-term clinical outcome are available. Compare all-cause mortality between two different sites of stimulation in the right ventricle. We retrospectively analyzed 150 consecutive patients who underwent pacemaker implantation because of complete AV block (spontaneous or after AV node ablation), symptomatic second-degree AV block, and symptomatic atrial fibrillation with slow ventricular response. All patients were implanted at the same institution with the standard technique. Apical stimulation was performed with a passive or active fixation lead and outflow tract pacing with an active fixation lead. Data collection period began in July 1999 and ended on December 2004. All patients included were greater than 70% ventricular paced during pacemaker follow-up. Patients older than 85 years were excluded from the analysis. Age, pacemaker mode, sex, ejection fraction, diabetes, and structural cardiac disease were analyzed. Mean age was 72+/-7 years (median 74 years, range 27-85 years), 101 (67%) were male, 56 had implanted a VVI PM, and 94 patients a DDD PM. Patients were divided into two groups: outflow tract (55 patients) and apical pacing (95 patients). Mean follow-up was 1,231+/-642 days (median 1,158 days, range 9 to 2,694 days), which ended on July 2007. Total mortality was examined with the Kaplan-Meier method to construct overall survival curves. Multivariate Cox proportional hazards regression models were performed. All patients or relatives were contacted personally or by phone. There were no major statistical differences in patient background between the two groups. During follow-up, 18 patients (32%) died in the outflow tract group and 49 (51%) in the apical group (log-rank p=0.02). Cox regression multivariate analysis showed that outflow tract pacing and a low left ventricular ejection fraction (<40%) were the only independent variables with significant correlation with survival (p=0.006 and 0.003, respectively). Outflow tract pacing appears to improve medium- and long-term survival. Prospective randomized trials with a greater amount of patients are necessary to confirm the findings of this study.

Functional columns in the primate prefrontal cortex revealed by optical imaging in vitro

Although the functional column has been implicated in the dorsolateral prefrontal cortex (DLPFC) of primates, its dynamics and even existence are still uncertain. We performed optical recording with a voltage-sensitive dye (RH482) in brain slices obtained from the principal sulcal region (area 46) of macaque monkeys. Columnar activity was evoked by electrical stimulation of the middle layer (lower layer III or layer IV); this activity consisted of two components: probably action potentials and excitatory postsynaptic potentials. The width of the columnar activity was saturated when the current intensity of stimulation exceeded a certain level, that is, approximately 900 μm at the peak with this intensity. The stimulation of different sites within the same slice activated different columnar activities with only slight overlaps. Furthermore, similar columnar activity appeared when a different site within the area with columnar activity was stimulated. These findings suggest that the primate DLPFC consists of functional columns formed by excitatory synaptic connections.

Writing-specific sites in frontal areas: a cortical stimulation study

The aim of this study was to determine whether cortical areas involved in the writing process are associated with reading or naming areas in patients undergoing surgery for brain tumors in frontal areas. This study was undertaken to spare all language areas found in patients during surgery. Fourteen patients (eight women and six men [mean age 47 years] of whom 12 were right handed, two left handed, 12 monolingual, and two bilingual) who harbored brain tumors in the left (11 patients) or right (three patients) frontal gyri or in rolandic areas, were tested by direct stimulation by using the awake surgery technique for direct brain mapping. Mapping of the frontal gyri was performed using naming, reading, and writing under dictation tasks in the appropriate language(s). Considerable individual variability in language organization among patients was observed. Interferences in writing were found during direct stimulation in the frontal gyri, in cortical sites common or not common to interferences in naming or reading. In dominant regions, patterns of writing dysfunctions were variable and included writing arrest, illegible script, letter omissions, and paragraphia. These dysfunctions were nonspecific (stimulation-induced eye movements) in nondominant frontal regions and in rolandic gyri (hand contractions). In the same patient, different writing impairments could sometimes be observed during stimulation of different sites. As is the case for naming or reading interference sites, writing interference sites could be extremely localized (1 cm2 in diameter). In this group of patients, writing interference sites found in Broca areas were associated with other sites of language interference, whereas writing-specific interference sites were found twice in the dominant middle frontal gyrus. In this series, we found that writing interference sites could be detected by direct cortical stimulation in dominant inferior and middle frontal gyri regardless of whether they were associated with naming or reading interference sites. Writing disorders elicited by direct stimulation in the frontal lobes are varied and probably depend on the functional status of the stimulated cortical area.

Characteristics of plateau activity during the latent period prior to epileptiform discharges in slices from rat piriform cortex.

The deep piriform region has an unusually high seizure susceptibility. Voltage imaging previously located the sites of epileptiform discharge onset in slices of rat piriform cortex and revealed the spatiotemporal pattern of development of two types of electrical activity during the latent period prior to discharge onset. A ramplike depolarization (onset activity) appears at the site of discharge onset. Onset activity is preceded by a sustained low-amplitude depolarization (plateau activity) at another site, which shows little if any overlap with the site of onset. Because synaptic blockade at either of these two sites blocks discharges, it was proposed that both forms of latent period activity are necessary for the generation of epileptiform discharges and that the onset and plateau sites work together in the amplification of electrical activity. The capacity for amplification was examined here by studying subthreshold responses in slices of piriform cortex using two different in vitro models of epilepsy. Under some conditions electrically evoked responses showed a nonlinear dependence on stimulus current, suggesting amplification by strong polysynaptic excitatory responses. The sites of plateau and onset activity were mapped for different in vitro models of epilepsy and different sites of stimulation. These experiments showed that the site of plateau activity expanded into deep layers of neighboring neocortex in parallel with expansions of the onset site into neocortex. These results provide further evidence that interactions between the sites of onset and plateau activity play an important role in the initiation of epileptiform discharges. The site of plateau activity showed little variation with different stimulation sites in the piriform cortex, but when stimulation was applied in the endopiriform nucleus (in the sites of onset of plateau activity), plateau activity had a lower amplitude and became distributed over a much wider area. These results indicate that in the initiation of epileptiform discharges, the location of the circuit that generates plateau activity is not rigidly defined but can exhibit flexibility.

Distal-proximal somatotopy in the human hand somatosensory cortex: a reappraisal.

The distal-proximal representation of the finger and palm in the first somatosensory cortex was reexamined. Somatosensory evoked magnetic fields (SEFs) were measured with a 37-channel first-order axial gradiometer system. Sensory stimulus comprising a 20-ms vibration at a frequency of 200 Hz was delivered to five successive sites in 3-cm increments along the distal-proximal direction over the volar surface of the right index finger and palm. Using a single dipole model, the sources and the signal strengths of the main peak (M50) of the SEFs were estimated. All of the sources were located in the 3b area. There were no statistically significant differences between the locations of dipoles evoked by stimulation of different sites. The results support those of our previous study using a 122-channel whole-head planar gradiometer system that orderly distal-proximal representation of the hand, as described in monkeys, is blurred in the adult human somatosensory cortex.

Voltage imaging of epileptiform activity in slices from rat piriform cortex: onset and propagation.

The piriform cortex is a temporal lobe structure with a very high seizure susceptibility. To investigate the spatiotemporal characteristics of epileptiform activity, slices of piriform cortex were examined by imaging electrical activity with a voltage-sensitive fluorescent dye. Discharge activity was studied for different sites of stimulation and different planes of slicing along the anterior-posterior axis. Epileptiform behavior was elicited either by disinhibition with a gamma-aminobutyric acid-A receptor antagonist or by induction with a transient period of spontaneous bursting in low-chloride medium. Control activity recorded with fluorescent dye had the same pharmacological and temporal characteristics as control activity reported previously with microelectrodes. Simultaneous optical and extracellular microelectrode recordings of epileptiform discharges showed the same duration, latency, and all-or-none character as described previously with microelectrodes. Under all conditions examined, threshold electrical stimulation applied throughout the piriform cortex evoked all-or-none epileptiform discharges originating in a site that included the endopiriform nucleus, a previously identified site of discharge onset. In induced slices, but not disinhibited slices, the site of onset also included layer VI of the adjoining agranular insular cortex and perirhinal cortex, in slices from anterior and posterior piriform cortex, respectively. These locations had not been identified previously as sites of discharge onset. Thus like the endopiriform nucleus, the deep agranular insular cortex and perirhinal cortex have a very low seizure threshold. Additional subtle differences were noted between the induced and disinhibited models of epileptogenesis. Velocity was determined for discharges after onset, as they propagated outward to the overlying piriform cortex. Propagation in other directions was examined as well. In most cases, velocities were below that for action potential conduction, suggesting that recurrent excitation and/or ephaptic interactions play a role in discharge propagation. Future investigations of the cellular and organizational properties of regions identified in this study should help clarify the neurobiological basis of high seizure susceptibility.

Contralateral Coordination and Retargeting of Limb Movements During Scratching in the Locust

ABSTRACT Locusts, Schistocerca gregaria, in common with many limbed vertebrates, can make directed scratching movements in response to tactile stimulation. For instance, stimulation of different sites on a wing elicits different movements that are accurately targeted so that the hindleg tarsus passes across the stimulus site. I have analysed these limb movements to define the ability of a locust to target stimulus sites correctly under a range of experimental conditions. In particular, I describe aspects of the behaviour that reveal possible neuronal pathways underlying the responses. These neuronal pathways will be the subject of further physiological analyses. Limb targeting during scratching is continuously graded in form; different patterns of movement are not separated by sharp transitions. The computation of limb trajectory takes into account the starting posture of the hindleg, so that different trajectories can be used to reach a common stimulus site from different starting postures. Moreover, the trajectories of the two hindlegs moving simultaneously from different starting postures in response to a single stimulus can be different, so that their tarsi converge onto the common stimulus site. Different trajectories can be used to reach a common stimulus site from the same start posture. Targeting information from a forewing is passed not only down the nerve cord to the ipsilateral hindleg but also across the nerve cord, so that the contralateral hindleg can also make directed movements. This contralateral transmission does not rely on peripheral sensory feedback. When the stimulus site moves during a rhythmical scratch, the targeting of subsequent cycles reflects this change. Both ipsilateral and contralateral hindlegs can retarget their movements. The trajectory of a single cycle of scratching directed towards a particular stimulus site can be modified after it has begun, so that the tarsus is redirected towards a new stimulus site.

Locomotor Patterns Elicited by Electrical Stimulation of the Brain Stem in the Mudpuppy

Microstimulation of the brain stem was performed in the mesencephalic mudpuppy. Repetitive (8-15 pps) stimulation of the lateral mesencephalic tegmentum elicited cyclic side-to-side movements of the tail or the body and stepping of the hindlimbs or forelimbs in different combinations. The association of all four components was most common, followed by the combined movements of the tail and the body; the tail, the hindlimbs, and the body; and the tail and the hindlimbs. Movements of the tail and the hindlimbs also occurred separately, but lateral undulation of the body was observed only in combinations, as was mainly stepping of the forelimbs. The cycle durations varied in different patterns: In particular, a cycle lasted 5 to 7 s for tail movements and 1.3 to 2 s for complete locomotion. Usually only one pattern was evoked by stimulating a particular site in the brain stem, but sometimes increasing the strength or frequency of stimulation involved an additional elementary synergy, thus forming a more complex pattern. Similar patterns could arise from stimulation of different sites. The order of involvement of components in the same complex pattern varied when stimuli were applied to different sites. The combinatorial composition and morphological specification are possible mechanisms of the broad repertoire of elicited locomotor patterns in the mudpuppy.