Lip Stimulation Research Articles

Transcranial alternating current stimulation over multiple brain areas with non-zero phase delays other than 180 degrees modulates visuospatial working memory performance

While zero-phase lag synchronization between multiple brain regions has been widely observed, relatively recent reports indicate that systematic phase delays between cortical regions reflect the direction of communications between cortical regions. For example, it has been suggested that a non-zero phase delay of electroencephalography (EEG) signals at the gamma frequency band between the bilateral parietal areas may reflect the direction of communication between these areas. We hypothesized that the direction of communication between distant brain areas might be modulated by multi-site transcranial alternating current stimulation (tACS) with specific phase delays other than 0° and 180°. In this study, a new noninvasive brain stimulation (NIBS) method called multi-site multi-phase tACS (msmp-tACS) was proposed. The efficacy of the proposed method was tested in a case study using a visuospatial working memory (VWM) paradigm in which the optimal stimulation conditions including amplitudes and phases of multiple scalp electrodes were determined using finite element analysis adopting phasor representation. msmp-tACS was applied over the bilateral intraparietal sulci (IPS) and showed that 80 Hz tACS with the phase for the right IPS leading that for the left IPS by 90° (= 3.125 ms) partialized VWM performance toward the right visual hemifield. The three stimulation conditions were synchronized, RL, and LR, which refers to stimulation condition with no phase lag, stimulation phase of right IPS (rIPS) leading left IPS (lIPS) by 90° and the stimulation of lIPS leading rIPS by 90°, respectively. The lateralization of VWM significantly shifted towards right visual hemifield under the RL condition compared to the synchronized and LR conditions. The shift in VWM was the result of the stimulation affecting both left and right visual hemifield trials to certain degrees, rather than significantly increasing or decreasing VWM capacity of a specific visual hemifield. Altered brain dynamics caused by msmp-tACS partialized VWM performance, likely due to modulation of effective connectivity between the rIPS and lIPS. Our results suggest that msmp-tACS is a promising NBS method that can effectively modulate cortical networks that cannot be readily modulated with conventional multi-site stimulation methods.

Effective connectivity and spatial selectivity-dependent fMRI changes elicited by microstimulation of pulvinar and LIP

The thalamic pulvinar and the lateral intraparietal area (LIP) share reciprocal anatomical connections and are part of an extensive cortical and subcortical network involved in spatial attention and oculomotor processing. The goal of this study was to compare the effective connectivity of dorsal pulvinar (dPul) and LIP and to probe the dependency of microstimulation effects on task demands and spatial tuning properties of a given brain region. To this end, we applied unilateral electrical microstimulation in the dPul (mainly medial pulvinar) and LIP in combination with event-related BOLD fMRI in monkeys performing fixation and memory-guided saccade tasks. Microstimulation in both dPul and LIP enhanced task-related activity in monosynaptically-connected fronto-parietal cortex and along the superior temporal sulcus (STS) including putative face patch locations, as well as in extrastriate cortex. LIP microstimulation elicited strong activity in the opposite homotopic LIP while no homotopic activation was found with dPul stimulation. Both dPul and LIP stimulation also elicited activity in several heterotopic cortical areas in the opposite hemisphere, implying polysynaptic propagation of excitation. Despite extensive activation along the intraparietal sulcus evoked by LIP stimulation, there was a difference in frontal and occipital connectivity elicited by posterior and anterior LIP stimulation sites. Comparison of dPul stimulation with the adjacent but functionally dissimilar ventral pulvinar also showed distinct connectivity. On the level of single trial timecourses within each region of interest (ROI), most ROIs did not show task-dependence of stimulation-elicited response modulation. Across ROIs, however, there was an interaction between task and stimulation, and task-specific correlations between the initial spatial selectivity and the magnitude of stimulation effect were observed. Consequently, stimulation-elicited modulation of task-related activity was best fitted by an additive model scaled down by the initial response amplitude. In summary, we identified overlapping and distinct patterns of thalamocortical and corticocortical connectivity of pulvinar and LIP, highlighting the dorsal bank and fundus of STS as a prominent node of shared circuitry. Spatial task-specific and partly polysynaptic modulations of cue and saccade planning delay period activity in both hemispheres exerted by unilateral pulvinar and parietal stimulation provide insight into the distributed interhemispheric processing underlying spatial behavior.

Time-dependent responses in brain activity to ongoing hot stimulation in burning mouth syndrome.

Burning mouth syndrome (BMS) is classified into idiopathic orofacial pain conditions. Although central and peripheral neuropathic mechanisms are believed to be involved, the etiology remains to be fully elucidated. The present study examined temporal brain responses to an ongoing hot stimulus to investigate the pain modulating system in patients with BMS. The thermal stimulation sequence comprised baseline (32°C, 40 s) to warm (40°C, 32 s) to baseline (32°C, 40 s) to hot (49°C, 32 s), which was repeated four times using a Peltier thermode. These warm and hot stimuli were applied on the right palm and right lower lip in two separate sessions. Functional magnetic resonance imaging data were acquired by recording echo-planar images with a block design. Brain activity induced by purely hot stimulation (49°C vs. 40°C) applied to the palm was more pronounced than that induced by lip stimulation and in patients with BMS compared with controls. Comparison of brain activity between the first 16 s and second 16 s of the stimulus revealed pronounced time-dependent facilitation in patients with BMS during lip stimulation. These findings indicate that the pain modulating system in patients with BMS is dysregulated and that the brain in BMS is highly sensitized to pain information originating from the trigeminal system.

Molecular correlates of separate components of training that contribute to long-term memory formation after learning that food is inedible in Aplysia.

Training Aplysia with inedible food for a period that is too brief to produce long-term memory becomes effective in producing memory when training is paired with a nitric oxide (NO) donor. Lip stimulation for the same period of time paired with an NO donor is ineffective. Using qPCR, we examined molecular correlates of brief training versus lip stimulation, of treatment with an NO donor versus saline, and of the combined stimuli producing long-term memory. Changes were examined in mRNA expression of Aplysia homologs of C/EBP, CREB1, CREB1α, CREB1β, and CREB2, in both the buccal and cerebral ganglia controlling feeding. Both the brief training and the NO donor increased expression of C/EBP, CREB1, CREB1α, and CREB1β, but not CREB2 in the buccal ganglia. For CREB1α, there was a significant interaction between the effects of the brief training and of the NO donor. In addition, the NO donor, but not brief training, increased expression of all of the genes in the cerebral ganglion. These findings show that the components of learning that alone do not produce memory produce molecular changes in different ganglia. Thus, long-term memory is likely to arise by both additive and interactive increases in gene expression.

Touching lips and hearing fingers: effector-specific congruency between tactile and auditory stimulation modulates N1 amplitude and alpha desynchronization.

Understanding the interactions between audition and sensorimotor processes is of theoretical importance, particularly in relation to speech processing. Although one current focus in this area is on interactions between auditory perception and the motor system, there has been less research on connections between the auditory and somatosensory modalities. The current study takes a novel approach to this omission by examining specific auditory-tactile interactions in the context of speech and non-speech sound production. Electroencephalography was used to examine brain responses when participants were presented with speech syllables (a bilabial sound /pa/ and a non-labial sound /ka/) or finger-snapping sounds that were simultaneously paired with tactile stimulation of either the lower lip or the right middle finger. Analyses focused on the sensory-evoked N1 in the event-related potential and the extent of alpha band desynchronization elicited by the stimuli. N1 amplitude over fronto-central sites was significantly enhanced when the bilabial /pa/ sound was paired with tactile lip stimulation and when the finger-snapping sound was paired with tactile stimulation of the finger. Post-stimulus alpha desynchronization at central sites was also enhanced when the /pa/ sound was accompanied by tactile stimulation of the lip. These novel findings indicate that neural aspects of somatosensory-auditory interactions are influenced by the congruency between the location of the bodily touch and the bodily origin of a perceived sound.

Reevaluation of reflex responses of the human masseter muscle to electrical lip stimulation.

We examined the reflex response of the human masseter muscle to electrical stimulation of the lip using both single motor unit and surface electromyogram based methods. Using the classical analysis methods, reflex response to mild electrical stimuli generated two distinct short-lasting inhibitions. This pattern may reflect the development of combinations of short- and long-latency inhibitory postsynaptic potentials as a result of the mildly painful electrical lip stimulation. However, this pattern appearing in the classical analysis methods may have developed as a consequence of earlier responses and may not be genuine. This study examined the genuineness of these responses using both the classical analysis methods and the discharge rate method to uncover the realistic postsynaptic potentials in human trigeminal motor nucleus. Using the discharge rate method, we found that the electrical lip stimulation only generated a long-lasting single or compound inhibitory response that is followed by late, long-lasting excitation. These findings have important implications on the redrawing of the neuronal pathways of the trigeminal nerve that are frequently used to judge neuromuscular disorders of the trigeminal region.NEW & NOTEWORTHY We examined the human masseter reflex response to electrical stimulation of lower lip to uncover realistic postsynaptic potentials in the trigeminal motor nucleus. We found that the stimulation generates a long-lasting single or compound inhibitory response that is followed by a late, long-lasting excitation. These findings have important implications on the redrawing of the neuronal pathways of the trigeminal nerve that are frequently used to judge neuromuscular disorders of the trigeminal region.

Spatial and Temporal Brain Responses to Noxious Heat Thermal Stimuli in Burning Mouth Syndrome

Burning mouth syndrome (BMS) is an idiopathic orofacial pain condition. Although the pathophysiology of BMS is not clearly understood, central and peripheral neuropathic mechanisms are thought to be involved. The authors compared brain response to noxious heat stimuli in 16 right-handed women with primary BMS and 15 sex- and age-matched right-handed healthy female controls. A thermal stimulus sequence of 32 °C to 40 °C to 32 °C to 49 °C was repeated 4 times in a cycle. Warm and noxious heat stimuli were delivered with a Peltier thermode placed on the right palm or right lower lip for 32 s each in a session. Functional magnetic resonance imaging data were obtained by recording echoplanar images with a block design. Statistical Parametric Mapping 8 software was used to analyze the data. Patients and controls both reported feeling more pain during palm stimulation than during lip stimulation. Repetition of noxious heat stimulus on the lower lip but not on the palm induced habituation in brain activity in the cingulate cortex without reduction in pain perception. Multiple regression analysis revealed a correlation between perceived pain intensity and suppression of brain activity in the anterior cingulate cortex when the repeated thermal sequence was applied at the lower lip. Furthermore, the response of the parahippocampal area differed in BMS patients and controls when the same repeated thermal sequence was applied at the palm. The authors’ findings indicate that BMS patients show specific brain responses due to impaired function of the central and peripheral nervous systems (clinical trial registration: UMIN000015002).

Differences in somatosensory processing due to dominant hemispheric motor impairment in cerebral palsy

BackgroundAlthough cerebral palsy (CP) is usually defined as a group of permanent motor disorders due to non-progressive disturbances in the developing fetal or infant brain, recent research has shown that CP individuals are also characterized by altered somatosensory perception, increased pain and abnormal activation of cortical somatosensory areas. The present study was aimed to examine hemispheric differences on somatosensory brain processing in individuals with bilateral CP and lateralized motor impairments compared with healthy controls. Nine CP individuals with left-dominant motor impairments (LMI) (age range 5–28 yrs), nine CP individuals with right-dominant motor impairments (RMI) (age range 7–29 yrs), and 12 healthy controls (age range 5–30 yrs) participated in the study. Proprioception, touch and pain thresholds, as well as somatosensory evoked potentials (SEP) elicited by tactile stimulation of right and left lips and thumbs were compared.ResultsPain sensitivity was higher, and lip stimulation elicited greater beta power and more symmetrical SEP amplitudes in individuals with CP than in healthy controls. In addition, although there was no significant differences between individuals with RMI and LMI on pain or touch sensitivity, lip and thumb stimulation elicited smaller beta power and more symmetrical SEP amplitudes in individuals with LMI than with RMI.ConclusionsOur data revealed that brain processing of somatosensory stimulation was abnormal in CP individuals. Moreover, this processing was different depending if they presented right- or left-dominant motor impairments, suggesting that different mechanisms of sensorimotor reorganization should be involved in CP depending on dominant side of motor impairment.

Evaluation of lip sensory disturbance using somatosensory evoked magnetic fields

ObjectiveTo evaluate lip sensory dysfunction in patients with inferior alveolar nerve injury by lip-stimulated somatosensory evoked fields (SEFs). MethodsSEFs were recorded following electrical lip stimulation in 6 patients with unilateral lip sensory disturbance and 10 healthy volunteers. Lip stimulation was applied non-invasively to each side of the lip with the same intensity using pin electrodes. ResultsAll healthy volunteers showed the earliest response clearly and consistently at around 25ms (P25m) and at least one of the following components, P45m, P60m, or P80m, over the contralateral hemisphere. The ranges of the peak latencies were 23–33, 42–50, 56–67, and 72–98ms for right-side stimulation and 23–34, 46–49, 52–68, and 71–90ms for left-side stimulation. Affected-side stimulation did not evoke P25m component in any patients, but invoked traceable responses in 5 patients whose latencies were 57, 89, 65, 53, and 54ms. Unaffected-side stimulation induced P25m in 2 patients at 27 and 25ms, but not in the other 4 patients. ConclusionThe P25m component of lip SEFs can be an effective parameter to indicate lip sensory abnormality. SignificanceLip sensory dysfunction can be objectively evaluated using magnetoencephalography.

Non-genital orgasms

Evidence from research and other sources is cited of orgasms elicited by imagery, stimulation of nipple, lips, mouth, anus, rectum, prostate and other body regions, in phantom limbs, during sleep, in response to brain and spinal cord stimulation, during childbirth, modulated by, and in response to, certain drugs and in relation to epileptic seizures. A concept of generalized neurological orgasmic processes involving recruitment, peak excitement and resolution is presented, of which genital orgasm is considered to be a special case.

TAC-Cell inputs to human hand and lip induce short-term adaptation of the primary somatosensory cortex

A new pneumatic tactile stimulator, called the TAC-Cell, was developed in our laboratory to non-invasively deliver patterned cutaneous stimulation to the face and hand in order to study the neuromagnetic response adaptation patterns within the primary somatosensory cortex (S1) in young adult humans. Individual TAC-Cells were positioned on the glabrous surface of the right hand, and midline of the upper and lower lip vermilion. A 151-channel magnetoencephalography (MEG) scanner was used to record the cortical response to a novel tactile stimulus which consisted of a repeating 6-pulse train delivered at three different frequencies through the active membrane surface of the TAC-Cell. The evoked activity in S1 (contralateral for hand stimulation, and bilateral for lip stimulation) was characterized from the best-fit dipoles of the earliest prominent response component. The S1 responses manifested significant modulation and adaptation as a function of the frequency of the punctate pneumatic stimulus trains and stimulus site (glabrous lip versus glabrous hand).

3-Dimensional eye-head coordination in gaze shifts evoked during stimulation of the lateral intraparietal cortex

Coordinated eye-head gaze shifts have been evoked during electrical stimulation of the frontal cortex (supplementary eye field (SEF) and frontal eye field (FEF)) and superior colliculus (SC), but less is known about the role of lateral intraparietal cortex (LIP) in head-unrestrained gaze shifts. To explore this, two monkeys (M1 and M2) were implanted with recording chambers and 3-D eye+ head search coils. Tungsten electrodes delivered trains of electrical pulses (usually 200 ms duration) to and around area LIP during head-unrestrained gaze fixations. A current of 200 μA consistently evoked small, short-latency contralateral gaze shifts from 152 sites in M1 and 243 sites in M2 (Constantin et al., 2007). Gaze kinematics were independent of stimulus amplitude and duration, except that subsequent saccades were suppressed. The average amplitude of the evoked gaze shifts was 8.46° for M1 and 8.25° for M2, with average head components of only 0.36 and 0.62° respectively. The head's amplitude contribution to these movements was significantly smaller than in normal gaze shifts, and did not increase with behavioral adaptation. Stimulation-evoked gaze, eye and head movements qualitatively obeyed normal 3-D constraints (Donders' law and Listing's law), but with less precision. As in normal behavior, when the head was restrained LIP stimulation evoked eye-only saccades in Listing's plane, whereas when the head was not restrained, stimulation evoked saccades with position-dependent torsional components (driving the eye out of Listing's plane). In behavioral gaze-shifts, the vestibuloocular reflex (VOR) then drives torsion back into Listing's plane, but in the absence of subsequent head movement the stimulation-induced torsion was “left hanging”. This suggests that the position-dependent torsional saccade components are preprogrammed, and that the oculomotor system was expecting a head movement command to follow the saccade. These data show that, unlike SEF, FEF, and SC stimulation in nearly identical conditions, LIP stimulation fails to produce normally-coordinated eye-head gaze shifts.

Altered somatosensory processing in trigeminal neuralgia

Trigeminal neuralgia (TN) is a pain state characterized by intermittent unilateral pain attacks in one or several facial areas innervated by the trigeminal nerve. The somatosensory cortex is heavily involved in the perception of sensory features of pain, but it is also the primary target for thalamic input of nonpainful somatosensory information. Thus, pain and somatosensory processing are accomplished in overlapping cortical structures raising the question whether pain states are associated with alteration of somatosensory function itself. To test this hypothesis, we used functional magnetic resonance imaging to assess activation of primary (SI) and secondary (SII) somatosensory cortices upon nonpainful tactile stimulation of lips and fingers in 18 patients with TN and 10 patients with TN relieved from pain after successful neurosurgical intervention in comparison with 13 healthy subjects. We found that SI and SII activations in patients did neither depend on the affected side of TN nor differ between operated and nonoperated patients. However, SI and SII activations, but not thalamic activations, were significantly reduced in patients as compared to controls. These differences were most prominent for finger stimulation, an area not associated with TN. For lip stimulation SI and SII activations were reduced in patients with TN on the contra- but not on the ipsilateral side to the stimulus. These findings suggest a general reduction of SI and SII processing in patients with TN, indicating a long-term modulation of somatosensory function and pointing to an attempt of cortical adaptation to potentially painful stimuli.

Somatosensory-Evoked Magnetic Fields in Examining Lip Area in Speech-Disordered Children

Magnetoencephalography (MEG) is a modern neurophysiological method to study brain activation after sensory stimulation. We aimed at determining the feasibility of MEG and somatosensory-evoked magnetic fields (SEFs) in assessing the lip area in speech-disordered children undergoing oral plate therapy (OPTH) to improve their articulation. Seven subjects (age range, 6-11 years) participated in the study. The speech was perceptually assessed, and the SEFs to tactile stimulation of the lip area were recorded before and after OPTH. Two patients did not attend the posttreatment MEG recording. Clinical perceptual analysis showed remarkable improvement of speech of the studied children after OPTH. Somatosensory-evoked magnetic fields were successfully recorded in 4 of these children, but no constant changes in the responses were found after the therapy.With this small number of patients, the possible modifications in the functioning of the cortical somatosensory area of the lip after OPTH remained undetected. The present method is, however, technically applicable in studying cortical responses to lip stimulation in speech-disordered children. Further studies using stimulation inside the mouth may provide more insight to the cortical effects of OPTH.

Responses to Tactile Stimulation in Deep Cerebellar Nucleus Neurons Result From Recurrent Activation in Multiple Pathways

In a previous study, we found that neurons in the deep cerebellar nuclei (DCN) respond to 5-ms brief facial tactile stimulation in rats anesthetized with ketamine-xylazine with multiphasic response patterns lasting over 200 ms. It remained unclear, however, to what extent these responses were shaped not only by ascending sensory input from the trigeminal nuclei but also by interactions with other major cerebellar afferent systems, in particular the inferior olive (IO) and cerebral cortex. In the present study, we recorded from the IO, cerebral cortex, cerebellar granule cell layer (GCL), and DCN during the presentation of 5-ms facial tactile stimuli to elucidate potential mechanisms of how extended DCN response patterns are generated. We found that tactile stimulation resulted in robust multiphasic local field potentials responses in the IO as well as in the activation of a wide region of the somatosensory cortex (SI) and the primary motor cortex (MI). DCN neurons responded to electrical stimulation of any of these structures (IO, SI, and MI) with complex temporal patterns strikingly similar to air-puff lip stimulation responses. Simultaneous recordings from multiple structures revealed that long-lasting activation patterns elicited in DCN neurons were based on recurrent network activation in particular between the IO and the DCN with a potential contribution of DCN rebound properties. These results are consistent with the hypothesis that sensory stimulation triggers a feedback network activation of cerebellum, IO, and cerebral cortex to generate temporal patterns of activity that may control the timing of behavior.

Frames of Reference for Gaze Saccades Evoked During Stimulation of Lateral Intraparietal Cortex

Previous studies suggest that stimulation of lateral intraparietal cortex (LIP) evokes saccadic eye movements toward eye- or head-fixed goals, whereas most single-unit studies suggest that LIP uses an eye-fixed frame with eye-position modulations. The goal of our study was to determine the reference frame for gaze shifts evoked during LIP stimulation in head-unrestrained monkeys. Two macaques (M1 and M2) were implanted with recording chambers over the right intraparietal sulcus and with search coils for recording three-dimensional eye and head movements. The LIP region was microstimulated using pulse trains of 300 Hz, 100-150 microA, and 200 ms. Eighty-five putative LIP sites in M1 and 194 putative sites in M2 were used in our quantitative analysis throughout this study. Average amplitude of the stimulation-evoked gaze shifts was 8.67 degrees for M1 and 7.97 degrees for M2 with very small head movements. When these gaze-shift trajectories were rotated into three coordinate frames (eye, head, and body), gaze endpoint distribution for all sites was most convergent to a common point when plotted in eye coordinates. Across all sites, the eye-centered model provided a significantly better fit compared with the head, body, or fixed-vector models (where the latter model signifies no modulation of the gaze trajectory as a function of initial gaze position). Moreover, the probability of evoking a gaze shift from any one particular position was modulated by the current gaze direction (independent of saccade direction). These results provide causal evidence that the motor commands from LIP encode gaze command in eye-fixed coordinates but are also subtly modulated by initial gaze position.

FMRI reflects functional connectivity of human somatosensory cortex

Unilateral sensory stimulation reliably elicits contralateral somatotopic activation of primary (SI) and secondary (SII) somatosensory cortex. There is an ongoing debate about the occurrence and nature of concomitant ipsilateral SI and SII activation. Here we used functional magnetic resonance imaging (fMRI) in healthy human subjects with unilateral tactile stimulation of fingers and lips, to compare somatosensory activation patterns from distal and proximal body parts. We hypothesized that fMRI in humans should reflect the functional connectivity of somatosensory cortex as predicted by animal studies. We show that both unilateral finger and lip stimulations activate contra- and ipsilateral SI and SII cortices with high detection frequency. Correlations of BOLD-signals to the applied hemodynamic reference function were significantly higher in contralateral as compared to ipsilateral SI and SII cortices for both finger and lip stimulation, reflecting strong contribution of contralateral thalamocortical input. Furthermore, BOLD-signal correlations were higher in SI than in SII activations on the contralateral but not on the ipsilateral side. While these asymmetries within and across hemispheres were consistent for finger and lip stimulations, indicating analogous underlying organizing principles, they were less prominent for lip stimulation. Somatotopic organization was detected in SI but not in SII representations of fingers and lips. These results qualitatively and quantitatively support the prevalent concepts of anatomical and functional connectivity in the somatosensory system and therefore may allow interpretation of sensory evoked fMRI signals in terms of normal human brain function. Thus, the assessment of human somatosensory function with fMRI may permit in the future investigations of pathological conditions.

Trigeminal somatosensory evoked magnetic fields to tactile stimulation

Objective To characterise the activation of the contra- and ipsilateral primary somatosensory cortex (SI) after tactile stimulation of the face. Methods Trigeminal somatosensory evoked magnetic fields (TSEFs) were recorded after tactile stimulation of the lower lip, cheek, chin and forehead in 11 healthy subjects. The responses were determined visually from the waveforms and modelled with equivalent current dipoles (ECDs). Results Contralateral SI responses were evoked in all subjects after lip stimulation, and in 91% and 64% after right and left cheek, 73% and 82% after chin and 64% and 27% after forehead stimulation. The responses usually showed an early double-peak wave pattern, the underlying sources localising to the SI. In addition, altogether 37 ipsilateral SI responses were evoked in eight subjects. Fourteen of these responses were amenable to ECD modelling and localised to ipsilateral SI. Conclusions Tactile stimulation of the lip area reliably activates the contralateral SI in normal subjects, but the success rate for other trigeminal areas is lower. Ipsilateral responses can be present after stimulation of any of the trigeminal branches in normal subjects. Significance Recording of TSEFs after tactile stimulation of particularly the lip area provides a non-invasive technique to study the function of the trigeminal nerve.

Magnetoencephalographic study for face representation in the human primary somatosensory cortex

To investigate the representation of facial skin area in the primary somatosensory cortex (SI), we recorded magnetoencephalography (MEG), the somatosensory-evoked magnetic fields (SEFs), by using tactile stimulation induced by air pressure applied to six points of facial skin (lateral and medial side of forehead, cheek and chin), lower lip and thumb. Equivalent current dipole (ECD) following thumb stimulation was located significantly more medial and superior to that following lip stimulation, which was consistent with Penfield's homunculus. In contrast, representation of six facial skin areas was located between the thumb and lip areas, and there was no significant difference of locations among six face points. This new finding was inconsistent with homunculus.

Electrical activity of caudal neurosecretory neurons in seawater and freshwater-adapted Platichthys flesus, in vivo

This study examined the electrical firing activity of neuroendocrine Dahlgren cells in the caudal neurosecretory system (CNSS) of the euryhaline flounder in vivo. Intracellular recordings revealed generally similar activity patterns and membrane properties to those previously reported in vitro. To investigate the potential role of the CNSS in osmoregulatory adaptation, extracellular, multiunit, recordings compared the activity patterns of Dahlgren cells in fully seawater- and freshwater-adapted fish. The proportion of cells showing bursting (as opposed to phasic or tonic) activity was greater in seawater-than in freshwater-adapted fish, as was the Correlation Index, a measure of the degree of correlation between firing activities of cells recorded simultaneously from the same preparation. Acute transfer of fish from seawater to freshwater gill perfusion led to recruitment of previously silent Dahlgren cells and a reduction in Correlation Index; freshwater to seawater transfer increased the Correlation Index. Severing the spinal cord anterior to the CNSS led to an increase in overall Dahlgren cell activity. Electrical stimulation of branchial nerve branches providing input to the brainstem, or tactile (pinch) stimulation of lips or fins, led to a reduction in CNSS activity lasting up to 500 s, indicating the presence of descending modulatory pathways from the brain. These results are consistent with a role for CNSS neuropeptides, urotensins, in supporting survival in a hypertonic, seawater, environment.