Event-related fMRI study of response inhibition

Event-related functional magnetic resonance imaging (erfMRI) was employed to measure the hemodynamic response during a Go/No-go task in 16 healthy subjects. The task was designed so that Go and No-go events were equally probable, allowing an unbiased comparison of cerebral activity during these two types of trials. In accordance with prediction, anterior cingulate was active during both the Go and No-go trials, dorsolateral and ventrolateral prefrontal cortex was more active during the No-go trials, while primary motor cortex, supplementary motor area, pre-motor cortex and cerebellum were more active during Go trials. These findings are consistent with the hypothesis that the anterior cingulate cortex is principally engaged in making and monitoring of decisions, while dorsolateral and ventral lateral prefrontal sites play a specific role in response inhibition.     

Heterotopic painful stimulation decreases the late component of somatosensory evoked potentials induced by electrical tooth stimulation

The purpose of this study was to determine the relationship between the late component of somatosensory evoked potentials (SEP) induced by electrical tooth stimulation and subjective pain estimation when heterotopically painful stimulation was delivered to humans. The noxious electrical conditioning stimuli were applied to the left median nerve in noxious session I and the right median nerve in noxious session II for 10 min. The amplitude of the late component and visual analogue scale (VAS) value were both decreased significantly by conditioning stimuli in both sessions. The maximum decreases in SEP amplitude and VAS value induced by conditioning stimuli were respectively 40.2 and 37.2% in noxious session I and 49.3 and 42.3% in noxious session II. After-effect was observed 5 min after removal of the conditioning stimuli. The rates of decrease were thus nearly the same and independent of the site of conditioning stimulation in noxious sessions I and II. The SEP amplitude was significantly correlated with VAS values. The present study revealed that SEP amplitude and subjective pain intensity estimated by VAS following electrical tooth stimulation can be decreased by noxious stimuli to hand. This finding that heterotopic painful stimulation attenuates experimentally-induced tooth pain suggests a triggering of diffuse noxious inhibitory control (DNIC) with after-effect in trigeminal region.     

Effect of transcutaneous electrical nerve stimulation (TENS) on central nervous system amplification of somatosensory input

The effect of transcutaneous electrical nerve stimulation (TENS) on the central nervous system amplification process was investigated focusing on the dorsal column-medial lemniscal pathway, because the dorsal column nucleus was recently shown to receive multiple sources of sensory information, including pain. Short latency somatosensory evoked potentials (SSEPs) were recorded in ten healthy normal volunteers. Amplitude changes in each SSEP component (the N9 brachial plexus potential, the P14 potential that originates from the cervicomedullary junction, spinal N13/P13 generated by the cervical dorsal horn and the cortical N20/P25 potential) were studied at stimulus strenghts ranging from the threshold (40% maximum stimulus) to 2.5 times the threshold (maximum). The findings suggest that sensory amplification begins at the P14 generator source near the cuneate nucleus. There was no statistically significant difference in sensory amplification between P14 and cortical N20/P25, indicating that the cuneate nucleus is the main site of the central amplifying process. When TENS was applied to the palm distal to the median nerve stimulation used for SSEP, cortical N20/P25 amplification disappeared, evidence that TENS suppresses the central amplification phenomenon, most probably at the level of the cuneate nucleus. Received: 29 October 1996 Received in revised form: 13 October 1997 Accepted: 6 November 1997     

Mapping of secondary somatosensory cortex activation induced by vibrational stimulation: an fMRI study

Sensory functional MRI was performed in seven normal volunteers at 1. 5 T using a vibratory stimulus applied to the pad of the first finger of the left hand. The data was normalized to a standard atlas, and individual and group statistical parametric maps were computed. Robust bilateral activation was demonstrated in the secondary somatosensory cortex (SII), indicating a bilateral representation of SII in humans. Greater maxima and activation volumes were achieved in contralateral SII as compared to SI. Sensory fMRI can provide a sensitive assay for probing the nature and function of SII in vivo.     

Scalp topography of somatosensory evoked potentials following electrical stimulation of femoral nerve

Up to 29 channels of somatosensory evoked potentials (SEPs) were recorded in 10 normal volunteers following unilateral femoral nerve (FN) and tibial nerve (TN) electrical stimulation. Typical short latency FN SEPs consisted of 6 components, P15, N19, P26, N34, P44 and N56. P15 and N19 were widely distributed on the scalp. The first localized scalp component, P26, was strictly postrolandic and distributed on the contralateral parietal scalp close to midline with a prerolandic phase reversal, N26. This scalp distribution is clearly different from the first localized potential of tibial nerve SEPs. N34 and P44 were maximal at the vertex with a distribution that spread to the ipsilateral central and parietal scalp. The amplitude of P26 increased and latency shortened with increasing stimulus intensity and both values plateaued after the stimulus intensity reached motor threshold. No correlation was found between the peak latency of P26 and body height.     

A clinical exercise system for paraplegics using functional electrical stimulation.

A low cost clinical exercise system was developed for the spinal cord injured, based on a bicycle ergometer and electrical stimulation. A pilot project was conducted, using the system, to examine the effects of stimulation induced cycling in long term paraplegics. The project comprised 2 phases of exercise, a strengthening phase involving a 12 week programme of electrical stimulation to the quadriceps and hamstrings and a 12 week cycling phase. Physiological, morphological and biochemical parameters were measured for each subject, at the beginning of the programme and following each phase. Results showed that a programme of stimulation induced lower limb exercise increased the exercise tolerance of all patients, as determined by a progressive increase in exercise time, cycling rate and exercise load. The enhanced exercise tolerance was a result of increases in local muscle strength and endurance. Increases in thigh muscle area and joint range of motion were recorded and all incomplete subjects reported an improvement in functional capabilities and general wellbeing.     

Event-related fMRI studies of episodic encoding and retrieval: Meta-analyses using activation likelihood estimation

The recent surge in event-related fMRI studies of episodic memory has generated a wealth of information about the neural correlates of encoding and retrieval processes. However, interpretation of individual studies is hampered by methodological differences, and by the fact that sample sizes are typically small. We submitted results from studies of episodic memory in healthy young adults, published between 1998 and 2007, to a voxel-wise quantitative meta-analysis using activation likelihood estimation [Laird, A. R., McMillan, K. M., Lancaster, J. L., Kochunov, P., Turkeltaub, P. E., & Pardo, J. V., et al. (2005). A comparison of label-based review and ALE meta-analysis in the stroop task. Human Brain Mapping, 25, 6–21]. We conducted separate meta-analyses for four contrasts of interest: episodic encoding success as measured in the subsequent-memory paradigm (subsequent Hit vs. Miss), episodic retrieval success (Hit vs. Correct Rejection), objective recollection (e.g., Source Hit vs. Item Hit), and subjective recollection (e.g., Remember vs. Know). Concordance maps revealed significant cross-study overlap for each contrast. In each case, the left hemisphere showed greater concordance than the right hemisphere. Both encoding and retrieval success were associated with activation in medial-temporal, prefrontal, and parietal regions. Left ventrolateral prefrontal cortex (PFC) and medial-temporal regions were more strongly involved in encoding, whereas left superior parietal and dorsolateral and anterior PFC regions were more strongly involved in retrieval. Objective recollection was associated with activation in multiple PFC regions, as well as multiple posterior parietal and medial-temporal areas, but not hippocampus. Subjective recollection, in contrast, showed left hippocampal involvement. In summary, these results identify broadly consistent activation patterns associated with episodic encoding and retrieval, and subjective and objective recollection, but also subtle differences among these processes.     

Modulation of proprioceptive feedback during functional electrical stimulation: an fMRI study

Functional electrical stimulation (FES) is sometimes used as a therapeutic modality in motor rehabilitation to augment voluntary motor drive to effect movement that would otherwise not be possible through voluntary activation alone. Effective motor rehabilitation should require that the central nervous system integrate efferent commands and appropriate afferent information to update the internal models of acquired skills. Here, we investigate whether FES‐evoked (FES‐ev) and FES‐assisted (FES‐as) movement are associated with the normal integration of motor commands and sensory feedback in a group of healthy participants during functional magnetic resonance imaging (fMRI). Sensory feedback was removed with a peripheral ischaemic nerve block while the participants performed voluntary (VOL), FES‐ev or FES‐as movement during fMRI. Before the peripheral nerve block, secondary somatosensory area (S2) activation was greater for the FES‐ev and FES‐as conditions than for the VOL condition. During the ischaemic nerve block, S2 activation was reduced for the FES‐ev condition but not for FES‐as and VOL conditions. The nerve block also reduced activation during FES in the primary somatosensory cortex and other motor areas including primary motor cortex, dorsal premotor cortex and supplementary motor area. In contrast, superior parietal lobule (area 7A) and precuneus activation was reduced as a consequence of the ischaemic nerve block in the VOL condition. These data suggest FES‐related S2 activation is mainly a sensory phenomenon and does not reflect integration of sensory signals with motor commands.     

Relation between palm and finger cortical representations in primary somatosensory cortex: A 7T fMRI study

Many studies focused on the cortical representations of fingers, while the palm is relatively neglected despite its importance for hand function. Here, we investigated palm representation (PR) and its relationship with finger representations (FRs) in primary somatosensory cortex (S1). Few studies in humans suggested that PR is located medially with respect to FRs in S1, yet to date, no study directly quantified the somatotopic organization of PR and the five FRs. Importantly, the link between the somatotopic organization of PR and FRs and their activation properties remains largely unexplored. Using 7T fMRI, we mapped PR and the five FRs at the single subject level. First, we analyzed the cortical distance between PR and FRs to determine their somatotopic organization. Results show that PR was located medially with respect to D5. Second, we tested whether the observed cortical distances would predict the relationship between PR and FRs activations. Using three complementary measures (cross‐activations, pattern similarity and resting‐state connectivity), we show that the relationship between PR and FRs activations were not determined by their somatotopic organization, that is, there was no gradient moving from D5 to D1, except for resting‐state connectivity, which was predicted by the somatotopy. Instead, we show that the representational geometry of PR and FRs activations reflected the physical structure of the hand. Collectively, our findings suggest that the spatial proximity between topographically organized neuronal populations do not necessarily predicts their functional properties, rather the structure of the sensory space (e.g., the hand shape) better describes the observed results.     

Phantom somatosensory evoked potentials following selective intraneural electrical stimulation in two amputees

Objective

The aim of the paper is to objectively demonstrate that amputees implanted with intraneural interfaces are truly able to feel a sensation in the phantom hand by recording “phantom” somatosensory evoked potentials from the corresponding brain areas.

Event-related fMRI of myoclonic jerks arising from dysplastic cortex

BACKGROUND: Malformations of cortical development can cause epileptiform activity and myoclonic jerks, yet EEG correlates of jerks can be difficult to obtain. METHODS: We studied a woman who had frequent episodes of persistent right-foot jerking since childhood. Ictal and interictal EEG had shown no localizing epileptiform activity. Functional imaging experiments were performed with concurrent video monitoring to document the timing of foot jerks. These studies mapped brain regions controlling voluntary right- and left-foot movements, and spontaneous right-foot jerks. RESULTS: High-resolution structural MR imaging revealed a dysplastic gyrus extending anteriorly off the left central sulcus. Event-related analysis of spontaneous jerks revealed prominent activation of the left precentral gyrus (right-foot motor area), bilateral medial frontal regions (supplementary motor area), and the dysplastic gyrus. Hemodynamic response modeling to foot jerks revealed the hemodynamic response peaked earlier in the dysplastic cortex and SMA regions than in the foot area. DISCUSSION: Event-related fMRI in a patient with spontaneous and induced epileptic foot jerks revealed brain regions active during jerks. The results of this analysis allowed us to tailor subsequent intracerebral recordings. Analysis of the timing of the hemodynamic response showed certain brain regions with an earlier rise in BOLD signal, suggesting a possible initiating role, or different hemodynamic response functions. Hemodynamic response timing should be considered carefully when interpreting event-related studies of epileptiform activity.     

Event-related fMRI analysis of the cerebral circuit for number comparison.

Cerebral activity during number comparison was studied with functional magnetic resonance imaging using an event-related design. We identified an extended network of task-related areas that showed a phasic activation following each trial, including anterior cingulate, bilateral sensorimotor areas, inferior occipito-temporal cortices, posterior parietal cortices, inferior and dorsolateral prefrontal cortices, and thalami. We then tested which of these areas were affected by number notation, numerical distance and response side, three variables that specifically target processes of visual identification, quantity manipulation and motor response in a serial-stage model of the number comparison task. Our results confirm the role of the right fusiform gyrus in digit identification processes, and of the inferior parietal lobule in the internal manipulation of numerical quantities.     

Intramuscular acupuncture-like electrical stimulation inhibits stretch reflexes in contralateral finger extensor muscles

Electro-acupuncture is one of many physical measures used to relieve musculoskeletal pain and to improve the associated restricted range of motion. Experiments were designed to determine whether or not acupuncture-like stimulation inhibits stretch reflexes in an arm extensor muscle in human volunteers. Surface electromyographic recordings were made on the right extensor digitorum communis muscle and averaging techniques were used to study the reflex responses to brief deflection of the finger with a solenoid-driven probe. The ratio M1:M2 of two components of the reflex was reduced during continuous acupuncture-like stimulation of the contralateral first dorsal interosseus and extensor digitorum communis muscles near their motor points (acupuncture points LI 4 and LI 11). Concomitant changes in skin temperature were observed on the forehead and in the arm in which acupuncture-like stimulation was used. In control experiments, when the acupuncture needles were inserted subcutaneously and stimulated with the same current parameters at distinctly uncomfortable intensities, no change in the reflexes occurred. These findings show that acupuncture-like stimulation exerts physiologic effects on the central nervous system, mediated presumably by muscle afferent fibers. The effects may be relevant to relief of muscle spasm and musculoskeletal pain, and restoration of mobility.     

Contralateral and ipsilateral responses in primary somatosensory cortex following electrical median nerve stimulation--an fMRI study.

OBJECTIVE: Ten healthy adult subjects were examined using functional magnetic resonance imaging (fMRI) to investigate responses in the contralateral and ipsilateral primary somatosensory cortex (SI) following electrical stimulation of the median nerve. METHODS: The right and left median nerves were stimulated alternately at the wrist in the different sessions. First, the location of the response in contralateral SI was identified following median nerve stimulation, and then, a spherical search volume with a 10mm radius centered on the region of the contralateral response was determined. Whether or not fMRI activation occurred within this sphere following ipsilateral stimulation was examined using a 3T MR imager. RESULTS: A response in contralateral SI was observed in 8 of the 10 subjects in right and left hemisphere. Responses in ipsilateral SI were observed in 6 of 8 subjects in right hemisphere, and the region of the response tended to be posterior to the contralateral region. On the other hand, in left hemisphere, the ipsilateral responses were found in three. CONCLUSIONS: In the present study, not only contralateral SI but also ipsilateral SI was activated following median nerve. The location of the ipsilateral activation was significantly more posterior than the contralateral one in right hemisphere. SIGNIFICANCE: The region of activation in ipsilateral SI was located in the posterior portion of post central gyrus, corresponding to around BA2 and 5 in human.     

Modulatory effects of somatosensory electrical stimulation on neural activity of the dorsal cochlear nucleus of hamsters

The effects of somatosensory electrical stimulation on the dorsal cochlear nucleus (DCN) activity of control and tone-exposed hamsters were investigated. One to three weeks after sound exposure and control treatment, multiunit activity was recorded at the surface of the left DCN before, during, and after electrical stimulation of the basal part of the left pinna. The results demonstrated that sound exposure induced hyperactivity in the DCN. In response to electrical stimulation, neural activity in the DCN of both control and exposed animals manifested four response types: S-S, suppression occurring during and after stimulation; E-S, excitation occurring during stimulation and suppression after; S-E, suppression occurring during stimulation and excitation after; and E-E, excitation occurring during and after stimulation. The results showed that there was a higher incidence of suppressive (up to 70%) than of excitatory responses during and after stimulation in both groups. In addition, there was a significantly higher degree of suppression after, rather than during stimulation. At high levels of electrical current, the degree of the induced suppression was generally higher during and after stimulation in exposed animals than in controls. The similarity of our results to those of previous clinical studies further supports the view that DCN hyperactivity is a direct neural correlate of tinnitus and that somatosensory electrical stimulation can be used to modulate DCN hyperactivity. Optimization of stimulation strategy through activating only certain neural pathways and applying appropriate stimulation parameters may allow somatosensory electrical stimulation to be used as an effective tool for tinnitus suppression.     

Cerebral blood flow regulation under activation of the primary somatosensory cortex during electrical stimulation of the forearm

Abstract

Coupling of neuronal activity to cerebral blood flow (CBF) is widely accepted, but the exact mechanism is still under investigation. We assessed the responses of CBF coupled with electrical activity over the primary somatosensory cortex (S-l) during electrical stimulation of the contralateral forearm in cats. CBF in S-I was monitored using laser-Doppler flowmetry (LDF), and electrical activity was recorded with a tungsten microelectrode. The effects of varying stimulus intensity and frequency were examined to assess the optimal stimulation parameters. CBF increased within 10 sec after onset of stimulation, sustained the plateau level, and returned to the pre-stimulus level after cessation of stimulation. The maximum response was obtained at 4 Hz under a constant intensity. Optimal stimulus intensity at 4 Hz ranged from 8 to 10 V. At intensity higher than 10 V, CBF increases reached a near-plateau level, while mean arterial blood pressure (MABP) decreased slightly. Electrical activity was recorded at the same restricted area where CBF increased. Low frequency components of the power spectrum of electrical activity increased as the CBF increase became greater. A tight coupling of CBF increases to neuronal activation is suggested, and CBF regulation may be affected by stimulation parameters. [Neurol Res 1999; 21: 579–584]     

Chronic electrical stimulation of transected peripheral nerves preserves anatomy and function in the primary somatosensory cortex

The structure and function of the central nervous system strongly depend on the organization and efficacy of the incoming sensory input. A disruption of somesthetic input severely alters the metabolic activity, electrophysiological properties and even gross anatomical features of the primary somatosensory cortex. Here we examined, in the rat somatosensory cortex, the neuroprotective and therapeutic effects of artificial sensory stimulation after irreversible unilateral transection of a peripheral sensory nerve (the infraorbital branch of the trigeminal nerve). The proximal stump of the nerve was inserted into a silicon tube with stimulating electrodes, through which continuous electrical stimulation was applied for 12 h/day (square pulses of 100 μs, 3.0 V, at 20 Hz) for 4 weeks. Deafferented animals showed significant decreases in cortical evoked potentials, cytochrome oxidase staining intensity (layers II–IV), cortical volume (layer IV) and number of parvalbumin‐expressing (layers II–IV) and calbindin‐D28k‐expressing (layers II/III) interneurons. These deafferentation‐dependent effects were largely absent in the nerve‐stimulated animals. Together, these results provide evidence that chronic electrical stimulation has a neuroprotective and preservative effect on the sensory cortex, and raise the possibility that, by controlling the physical parameters of an artificial sensory input to a sectioned peripheral nerve, chronically deafferented brain regions could be maintained at near‐‘normal’ conditions. Our findings could be important for the design of sensory neuroprostheses and for therapeutic purposes in brain lesions or neural degenerative processes.     

Event-related fMRI: comparison of conditions with varying BOLD overlap

Recently, event-related fMRI-experiments have been reported in which subsequent trials were separated by only 2 sec or less. Because the BOLD response needs 10 sec and longer to return to baseline, the event-related signal in these experiments has to be extracted from the overlapping responses elicited by successive trials. Usually it is assumed that this convolved signal is a summation of the overlapping BOLD responses. We tested this assumption by comparing event-related signals in conditions with little and with substantial BOLD overlap in two fMRI experiments of a task-switching paradigm. We analyzed the difference in the activational time course elicited by a critical task and a baseline task when trials of both tasks were separated by intertrial intervals of 15 sec or when the critical trials were embedded in a stream of baseline trials with ISI = 1 sec. The change of the BOLD signal elicited by the critical trials showed a high correspondence between both experiments in five out of six cortical ROI. Our data support the view that BOLD overlap leads to largely linear signal changes. In the present study, task-related increases in the BOLD response were detected equally well with substantial BOLD overlap as with mostly nonoverlapping BOLD responses.