Neuronal activity in monkey primary somatosensory cortex is related to expectation of somatosensory and visual go-cues

The present study was to investigate whether neuronal activity in primary somatosensory cortical areas (SI) differs when monkeys expect go-cues of different sensory modalities. Two monkeys made wrist extensions and flexions after steadily holding wrist at a center position. Movements were guided by increases in vibration to the monkey's palm (VIB), visual targets (VIS), or both in combination (COM). Neuronal activity recorded in SI during the early and late phases (i.e., the first and last 250 ms) of the instructed delay periods (IDP) were analyzed. Of 406 neurons recorded during all three paradigms, 263 (64.8%) showed significant changes in firing rates (FR) between the early and late IDP phases during either VIB or VIS trials and were selected for further analyses. The selected neurons were classified as VIB- or VIS-biased, depending on the paradigm (VIB or VIS) in which the greater FR changes occurred. Both increases and decreases in FRs were observed during the analyzed epochs. Most VIB-biased neurons showed the biggest FR changes during VIB trials and the least during VIS trials. Conversely, most VIS-biased neurons had the biggest FR changes during VIS trials and the least during VIB trials. For both VIB- and VIS-biased neurons, however, the FR changes were intermediate during COM trials. These results suggest that SI neurons play an important role in initiating/executing wrist movements. Neurons involved in wrist movements showed biases to the modality of cueing signals. Most SI neurons were biased to only one sensory modality. The expectation-related FR changes suggest different involvement by SI in movement initiation when tasks are guided by vibratory and visual signals.     

Epileptiform activity in the somatosensory cortex of rats with trigeminal neuralgia

Laboratory of Pathophysiology of Pain, Research Institute of General Pathology and Pathological Physiology, Russian Academy of Medical Sciences, Moscow. Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 114, No. 8, pp. 126–128, August, 1992.     

Baseline and evoked spike activity in neurons in embryonic transplants of the somatosensory cortex in rats

The aim of the present work was to study the nature of the baseline and evoked spike activity of neurons in embryonic transplants four months after homotopic allotransplantation into the whisker representation zone of the somatosensory cortex of the recipient rat brain (the barrel field). These studies showed that the instantaneous mean spike frequency of neuron activity was decreased in neural transplants as compared with the somatosensory cortex of control rats, while the latent period of evoked cell activity was longer. In addition, the pattern of evoked activity in transplant neurons was characterized by an increased frequency of spike generation or alternation of periods of activation and decreased spike frequency with subsequent recovery to the initial level, this being similar to the pattern seen in neurons in the whisker representation zone of the somatosensory cortex in control rats. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 91, No. 5, pp. 473–480, May, 2005.     

Spatiotemporal characteristics of pain-associated neuronal activities in primary somatosensory cortex induced by peripheral persistent nociception

The primary somatosensory cortex (S1 area) is one of the key brain structures for central processing of somatic noxious information to produce pain perception. However, so far, the spatiotemporal characteristics of neuronal activities associated with peripheral persistent nociception have rarely been studied. In the present report, we used c-Fos as a neuronal marker to analyze spatial and temporal patterns of pain-related neuronal activities within the S1 area of rats subjecting to subcutaneous (s.c.) injection of bee venom (BV) solution, a well-established animal model of persistent pain. In naïve and saline-treated rats, c-Fos-labeled neurons were diffusely and sparsely distributed in the hindlimb region of S1 area. Following s.c. BV injection, c-Fos-labeled neurons became densely increased in superficial layers (II–III) and less increased in deep layers (IV–VI). The mean number of c-Fos positive neurons in the layers II–III began to increase at 1 h and reached a peak at 2 h after BV treatment that was followed by a gradual decrease afterward. The time course of c-Fos expression in the layers IV–VI was in parallel with that of the superficial layers, but with a much lower density and magnitude. The present results demonstrated that BV-induced peripheral persistent nociception could evoke increased neuronal activities in the S1 area with predominant localization in layers II–III.     

Effects of electrical stimulation of somatosensory and motor areas of the cerebral cortex on neurones of the pontine nuclei in squirrel monkeys

The aim of the present investigation was to determine whether neurones in the pontine nuclei receive convergent inputs from subdivisions of somatosensory and motor cortex and whether these neurones display receptive fields. Extracellular single unit recordings were made in squirrel monkeys under N₂O-thiamylal anaesthesia. Sixty-nine neurones identified by antidromic invasion from the contralateral brachium pontis were subdivided into the following classes: (1) fifteen neurones without an input from the cortical sites tested; (2) twenty-two neurones with an input from one cortical site; (3) eighteen neurones with an input from two cortical sites; (4) fourteen neurones with multiple cortical inputs. Cells with a given cortical input appeared to be randomly distributed in the transverse plane of the pons. Twenty neurones were excited by passive movements of the limbs or various cutaneous stimuli; the majority of the receptive fields were large. Fifteen percent of the neurones were activated by collaterals of corticospinal fibres.     

Monkey primary somatosensory cortical activity during the early reaction time period differs with cues that guide movements

Vibration-related neurons in monkey primary somatosensory cortex (SI) discharge rhythmically when vibratory stimuli are presented. It remains unclear how functional information carried by vibratory inputs is coded in rhythmic neuronal activity. In the present study, we compared neuronal activity during wrist movements in response to two sets of cues. In the first, movements were guided by vibratory cue only (VIB trials). In the second, movements were guided by simultaneous presentation of both vibratory and visual cues (COM trials). SI neurons were recorded extracellularly during both wrist extensions and flexions. Neuronal activity during the instructed delay period (IDP) and the early reaction time period (RTP) were analyzed. A total of 96 cases from 48 neurons (each neuron contributed two cases, one each for extension and flexion) showed significant vibration entrainment during the early RTPs, as determined by circular statistics (Rayleigh test). Of these, 50 cases had cutaneous (CUTA) and 46 had deep (DEEP) receptive fields. The CUTA neurons showed lower firing rates during the IDPs and greater firing rate changes during the early RTPs when compared with the DEEP neurons. The CUTA neurons also demonstrated decreases in activity entrainment during VIB trials when compared with COM trials. For the DEEP neurons, the difference of entrainment between VIB and COM trials was not statistically significant. The results suggest that somatic vibratory input is coded by both the firing rate and the activity entrainment of the CUTA neurons in SI. The results also suggest that when vibratory inputs are required for successful task completion, the activity of the CUTA neurons increases but the entrainment degrades. The DEEP neurons may be tuned before movement initiation for processing information encoded by proprioceptive afferents.     

Responses of infragranular neurons in the rat primary somatosensory cortex to forepaw and hindpaw tactile stimuli

Infragranular layers constitute the main output of the primary somatosensory cortex and represent an important stage of cortico-cortical and cortico-subcortical integration. We have previously used chronic multiple single-unit recordings to study the spatiotemporal structure of tactile responses of infragranular neurons within the forepaw cortical representation in rats [Tutunculer B, Foffani G, Himes BT, Moxon KA (2006) Structure of the excitatory receptive fields of infragranular forelimb neurons in the rat primary somatosensory cortex responding to touch. Cereb Cortex 16:791-810]. Here we extend our understanding of this structure by studying the overlap between the forepaw and hindpaw cortical representations. We recorded 204 responsive neurons in chronic experiments from eight anesthetized rats. Overall, only 23% of neurons responded exclusively to one paw, 52% of neurons responded to two paws, 19% of neurons responded to three paws, and 5% of neurons responded to all four paws. Quantitative measures of response magnitudes and latencies revealed the following main results. (1) The responses of forepaw neurons overall displayed greater magnitudes and shorter latencies than the responses of hindpaw neurons. (2) The responses to ipsilateral stimuli displayed smaller magnitudes, and longer-and more variable-latencies than the responses to contralateral stimuli. (3) The responses of forepaw neurons to hindpaw stimuli displayed smaller magnitudes and longer latencies than the responses to forepaw stimuli, whereas the responses of hindpaw neurons to forepaw stimuli displayed smaller magnitudes but similar latencies compared with the responses to hindpaw stimuli. These results show that the spatiotemporal structure of tactile responses of infragranular neurons extends across all four paws, and provide the basic architecture for studying physiological integration and pathophysiological reorganization of tactile information in the infragranular layers of the rat primary somatosensory cortex.     

Identification of two populations of corticothalamic neurons in cat primary somatosensory cortex

Summary Extracellular and intracellular recordings of corticothalamic (CT) cells were performed in the primary somatosensory cortex of the cat. CT neurons were antidromically activated by electrically stimulating the ventroposterior lateral (VPL) nucleus of the thalamus and were classified into two types according to their physiological properties. Type 1 had no spontaneous activity and no identifiable somatic receptive field. Type 2 fired action potentials spontaneously and responded to mechanical stimulation of the skin or underlying tissues. Axonal conduction velocities were slower for type 1 cells and their cell bodies were located slightly deeper in the cortex than those of type 2 cells. Both types of CT neurons exhibited inhibitory postsynaptic potentials in response to VPL stimulation but an early synaptic excitation and rebound discharge was observed almost exclusively in type 2 cells. These results suggest that only type 2 CT cells can modify the activity of thalamic neurons through a corticothalamic feedback loop.     

Long-term increases in neuronal activity in the motor cortex evoked by simultaneous stimulation of the thalamus and somatosensory cortex in cats

Experiments on anesthetized cats were used to study the activity of motor cortex neurons (field 4γ) in response to separate and simultaneous stimulation of the ventrolateral nucleus of the thalamus and the somatosensory cortex (field 2) of the brain. Long-term potentiation of motor cortex neuron activity in response to simultaneous stimulation of the ventrolateral nucleus and somatosensory cortex arose only in regions receiving corticocortical projections from the stimulation site in the somatosensory cortex of the brain, while regions lacking corticocortical projections from the somatosensory cortex showed no such effect. Experiments demonstrated that the duration of increased motor cortex neuron activity following stimulation of the ventrolateral nucleus of the thalamus and somatosensory cortex was greater than one hour after recording was started. These data led to the conclusion that simultaneous stimulation of corticocortical and thalamocortical afferents can alter the level of neuronal activity in the motor cortex only in regions with convergent sensory inputs from the thalamus and somatosensory cortex of the brain. Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 84, No. 5–6, pp. 460–468, May–June, 1998.     

Response of neurons in primary somatosensory cortex of cat following prolonged exposure to strong sinusoidal mechanical stimuli

Psychophysical studies in humans have demonstrated adaptation of the mechanoreceptive submodalities of flutter and vibration after prolonged presentation of a strong adapting, or conditioning, stimulus. In our studies we recorded from single neurons in cat primary somatosensory cortex, and followed a paradigm in which the response of a single unit was measured before and after the presentation of a strong conditioning stimulus. Our findings show no adaptive response in the 30 sec period immediately after cessation of the conditioning stimulus, and suggest that other parallel ascending pathways or somatosensory cortical areas other than SI account for these psychophysical observations.     

Movement induced modulation of afferent transmission to single neurons in the ventroposterior thalamus and somatosensory cortex in rat

Summary Single neurons were simultaneously recorded in the forepaw areas of the primary somatosensory (SI) cortex and ventroposterolateral (VPL) thalamus of awake rats during rest and running behaviors. Movement dependent changes in somatic sensory transmission were tested by generating post-stimulus histograms of these neurons' responses to stimulation through electrodes chronically implanted under the skin of the forepaw, while the aminal ran on a timed treadmill. As viewed in post-paw-stimulus histograms, the evoked unit responses (EURs) could be differentiated into short (4.5 ± 0.1−10.9 ± 0.2 ms) and longer (12.9 ± 0.4 31.3 ± ± 0.9 ms) latency components (“SEURs” and “LEURs”, respectively). The magnitudes of firing during these responses were measured and normalized as percent increases over background firing. By comparison with resting behavior, treadmill movement suppressed both SEURs and LEURs in the thalamus, as well as the cortex. The SEURs, however, were much more strongly suppressed in the SI cortex (−48.3 ± 2.7%) than in the VPL thalamus (−28.1 ± 6.7%). By contrast, similar magnitudes of suppression of LEURs were found in the SI (−25.8 ± 8.6%) and VPL (−26.5 ± 11.1%). These results suggest that the suppression of LEURs observed in the SI cortex may result from modulatory actions on subcortical circuits. Major suppression of SEURs, on the other hand, may occur intracortically, with a minor component ocurring subcortically. Thus, VPL thalamus and SI cortex in the rat appear to be differentially subject to movement related modulation of sensory transmission.     

Motor effects produced by stimulation of secondary somatosensory (SII) cortex in the monkey

Summary Threshold for evoking movements by microstimulation of the second somatosensory area of the cynomolgus monkey's cortex to intracortical microstimulation was examined. Motor effects were obtained contralateral to the side of stimulation, in a region histologically verified to be in grey matter deep in the sylvian cortex, and which corresponds to the second somatosensory cortex. The thresholds were low but higher than for movements evoked by stimulation of the motor cortex. The results are explained in terms of increased specialization of the motor cortex for movements in the monkey compared with the cat.     

Navigated transcranial magnetic stimulation of the primary somatosensory cortex impairs perceptual processing of tactile temporal discrimination

Previous studies indicate that transcranial magnetic stimulation (TMS) with biphasic pulses applied approximately over the primary somatosensory cortex (S1) suppresses performance in vibrotactile temporal discrimination tasks; these previous results, however, do not allow separating perceptual influence from memory or decision-making. Moreover, earlier studies using external landmarks for directing biphasic TMS pulses to the cortex do not reveal whether the changes in vibrotactile task performance were due to action on S1 or an adjacent area. In the present study, we determined whether the S1 area representing a cutaneous test site is critical for perceptual processing of tactile temporal discrimination. Electrical test pulses were applied to the thenar skin of the hand and the subjects attempted to discriminate single from twin pulses. During discrimination task, monophasic TMS pulses or sham TMS pulses were directed anatomically accurately to the S1 area representing the thenar using magnetic resonance image-guided navigation. The subject's capacity to temporal discrimination was impaired with a decrease in the delay between the TMS pulse and the cutaneous test pulse from 50 to 0 ms. The result indicates that S1 area representing a cutaneous test site is involved in perceptual processing of tactile temporal discrimination.     

Neuronal activity in primary motor cortex differs when monkeys perform somatosensory and visually guided wrist movements

This study was designed to investigate how activity patterns of primary motor cortical (MI) neurons change when monkeys perform the same movements guided by somatosensory and/or visual cues. Two adult male rhesus monkeys were trained to make wrist extensions and flexions after holding a steady position during an instructed delay period lasting 0.5–2.0 s. Monkeys held against a 0.07 Nm load that opposed flexion movements. Wrist movements were guided by vibratory cues (VIB-trials), visual cues (VIS-trials), or both in combination (COM-trials). Extracellular recordings of 188 MI neurons were made during all three paradigms. Individual neurons were counted twice, once for each movement direction, yielding 376 cases. All neurons had significant task-related activity (TRA) changes relative to delay period activity during at least one of the three paradigms. TRA was analyzed to determine if it was different as a function of the sensory cue(s) that initiated movement and that specified movement endpoints. Cases were grouped by whether the TRA changes were greater in VIB- or VIS-trials; this defined their “bias”. One hundred and eighteen cases (31.4%) had greater TRA changes in VIB-trials (Vb-neurons), whereas 185 (49.2%) showed greater TRA changes in VIS-trials (Vs-neurons). The remaining 73 cases (19.4%) had similar TRA changes in VIB- and VIS-trials (Nb-neurons). For Vb- and Vs-neurons, earlier TRA onsets and greater TRA changes were observed in the trials for which these neurons were biased. During the COM-trials, the TRA was intermediate. During the trials for which the activity was not biased, the TRA was the least. For Nb-neurons, no significant TRA differences were observed across paradigms. TRA changes of MI neurons may represent movement planning-related inputs from other central, presumably cortical, sources as well as contribute to motor outflow from the cortex. These data suggest that Vb- and Vs-neurons are affected differently by somatosensory- and visually related central inputs, resulting in different TRAs, even for essentially identical movements. Such differences may depend not only on the type of sensory information that initiates movement but also whether that information specifies movement endpoints or might interfere with movement monitoring.     

Attenuation of N2 amplitude of laser-evoked potentials by theta burst stimulation of primary somatosensory cortex

Theta burst stimulation (TBS) is a special repetitive transcranial magnetic stimulation (rTMS) paradigm, where bursts of low-intensity stimuli are applied in the theta frequency. The aim of this study was to investigate the effect of neuronavigated TBS over primary somatosensory cortex (SI) on laser-evoked potentials (LEPs) and acute pain perception induced with Tm : YAG laser stimulation. The amplitude changes of the N1, N2, and P2 components of LEPs and related subjective pain rating scores of 12 healthy subjects were analyzed prior to and following continuous TBS (cTBS), intermittent TBS (iTBS), intermediate TBS (imTBS), and sham stimulation. Our results demonstrate that all active TBS paradigms significantly diminished the amplitude of the N2 component, when the hand contralateral to the site of TBS was laser-stimulated. Sham stimulation condition had no significant effect. The subjective pain perception also decreased during the experimental sessions, but did not differ significantly from the sham stimulation condition. The main finding of our study is that TBS over SI diminished the amplitude of the N2 component evoked from the contralateral side without any significant analgesic effects. Furthermore, imTBS produced responses similar to those observed by other forms of TBS induced excitability changes in the SI.     

The hemodynamic component of compensation in the brain after unilateral blocking of the somatosensory cortex

In experiments on anesthetized and waking cats the dynamics of the cerebral blood flow was investigated by a thermoelectric method in one hemisphere during experimental injury to the somatosensory area of the opposite hemisphere. Temporary cold blocking of this area of the cortex gives rise to definite hemodynamic distorbances in the opposite hemisphere, namely a biphasic vascular response: an initial decrease in the blood supply followed by a long after-effect of an increase in the blood flow. Similar vascular responses also were observed after unilateral extirpation of the somatosensory cortex. Vascular responses of this type are evidence of increased activity of the cortical structures in the intact hemisphere and can be regarded as a compensatory response to local injury of particular areas of the cortex.Laboratory of Pathophysiology of Neurohumoral Regulation, Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. M. Chernukh.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 87, No. 4, pp. 299–301, April, 1979.