Different Patterns of Attention Modulation in Early N140 and Late P300 sERPs Following Ipsilateral vs. Contralateral Stimulation at the Fingers and Cheeks

Intra-hemispheric interference has been often observed when body parts with neighboring representations within the same hemisphere are stimulated. However, patterns of interference in early and late somatosensory processing stages due to the stimulation of different body parts have not been explored. Here, we explore functional similarities and differences between attention modulation of the somatosensory N140 and P300 elicited at the fingers vs. cheeks. In an active oddball paradigm, 22 participants received vibrotactile intensity deviant stimulation either ipsilateral (within-hemisphere) or contralateral (between-hemisphere) at the fingers or cheeks. The ipsilateral deviant always covered a larger area of skin than the contralateral deviant. Overall, both N140 and P300 amplitudes were higher following stimulation at the cheek and N140 topographies differed between fingers and cheek stimulation. For the N140, results showed higher deviant ERP amplitudes following contralateral than ipsilateral stimulation, regardless of the stimulated body part. N140 peak latency differed between stimulated body parts with shorter latencies for the stimulation at the fingers. Regarding P300 amplitudes, contralateral deviant stimulation at the fingers replicated the N140 pattern, showing higher responses and shorter latencies than ipsilateral stimulation at the fingers. For the stimulation at the cheeks, ipsilateral deviants elicited higher P300 amplitudes and longer latencies than contralateral ones. These findings indicate that at the fingers ipsilateral deviant stimulation leads to intra-hemispheric interference, with significantly smaller ERP amplitudes than in contralateral stimulation, both at early and late processing stages. By contrast, at the cheeks, intra-hemispheric interference is selective for early processing stages. Therefore, the mechanisms of intra-hemispheric processing differ from inter-hemispheric ones and the pattern of intra-hemispheric interference in early and late processing stages is body-part specific.

Thalamic encoding of complex sensory patterns and its possible role in cognition

The function of the higher-order sensory thalamus remains unresolved. Here, POm nucleus was examined by in vivo extracellular recordings across a range of complex sensory patterns. We found that POm was highly sensitive to multiwhisker stimuli involving complex spatiotemporal interactions. The dynamical spatiotemporal structure of sensory patterns and the different complexity of their parts were accurately reflected in precise POm activity changes. Importantly, POm was also able to respond to ipsilateral stimulation and was implicated in the representation of bilateral tactile events by integrating simultaneous signals arising from both whisker pads. We found that POm nuclei are mutually connected through the cortex forming a functional POm-POm loop. We unravelled the nature and content of the messages travelling through this loop showing that they were ‘structured patterns of sustained activity’. These structured messages were transmitted preserving their integrated structure. The implication of different cortical areas was investigated revealing that S1 plays a protagonist role in this functional loop. Our results also demonstrated different laminar implication in the processing of sustained activity in this cortical area and its transmission between hemispheres. We propose a theoretical model in which these ‘structured patterns of sustained activity’ generated by POm may play important roles in perceptual, motor and cognitive functions. From a functional perspective, this proposal, supported by the results described here, provides a novel theoretical framework to understand the implication of the thalamus in cognition. In addition, a profound difference was found between VPM and POm functioning. The hypothesis of Complementary Components is proposed here to explain it.HighlightsPOm is implicated in the representation of complex sensory patterns.POm is implicated in the encoding of bilateral tactile events.POm nuclei are mutually connected through the cortex forming a functional POm-POm loop.‘Structured patterns of sustained activity’ travelling through the loopAbstract Figure

Changes in Cortical Auditory Evoked Potentials by Ipsilateral, Contralateral and Binaural Speech Stimulation in Normal-Hearing Adults

Objectives. Cortical auditory evoked potentials (CAEPs) have been used to examine auditory cortical development or changes in patients with hearing loss. However, there have been no studies analyzing CAEP responses to the different sound stimulation by different stimulation sides. We characterized changes in normal CAEP responses by stimulation sides in normal-hearing adults.Methods. CAEPs from the right auditory cortex were recorded in 16 adults following unilateral (ipsilateral and contralateral) and bilateral sound stimulation using three speech sounds (/m/, /g/, and /t/). Amplitudes and latencies of the CAEP peaks in three conditions were compared.Results. Contralateral stimulation elicited larger P2-N1 amplitudes (sum of P2 and N1 amplitudes) than ipsilateral stimulation regardless of the stimulation sounds, mostly due to the larger P2 amplitudes obtained, but elicited comparable P2-N1 amplitudes to bilateral stimulation. Although the P2-N1 amplitudes obtained with the three speech sounds were comparable following contralateral stimulation, the /m/ sound elicited the largest P2-N1 amplitude in ipsilateral stimulation condition due to the largest N1 amplitude obtained, whereas /t/ elicited larger a P2-N1 amplitude than /g/ in bilateral stimulation condition due to a larger P2 amplitude.Conclusion. Spectrally different speech sounds and input sides are encoded differently at the cortical level in normal-hearing adults. Standardized speech stimuli, as well as specific input sides of speech, are needed to examine normal development or rehabilitation-related changes of the auditory cortex in the future.

The striking effects of deep cerebellar stimulation on generalized fixed dystonia: case report

Cerebellar neuromodulation could influence the pathological abnormalities of movement disorders through several connections between the cerebellum and the basal ganglia or other cortices. In the present report, the authors demonstrate the effects of cerebellar deep brain stimulation (DBS) on a patient with severe generalized fixed dystonia (FD) that was refractory to bilateral pallidotomy and intrathecal baclofen therapy. A previously healthy 16-year-old girl presented with generalized FD. Bilateral pallidotomy and intrathecal baclofen therapy had failed to resolve her condition, following which she received DBS through the bilateral superior cerebellar peduncle (SCP) and dentate nucleus (DN). Ipsilateral stimulation of the SCP or DN improved the FD, and the ability of DBS administered via the SCP to relax muscles was better than that of DN DBS. A considerable improvement of generalized FD, from a bedridden state to a wheelchair-bound state, was observed in the patient following 6 months of chronic bilateral DBS via the SCP; moreover, the patient was able to move her arms and legs. The findings in the present case suggest that neuromodulation of deep cerebellar structures is a promising treatment for FD that is refractory to conventional treatments.

Alteration of Duration Mismatch Negativity Induced by Transcranial Magnetic Stimulation Over the Left Parietal Lobe

Mismatch negativity (MMN) is generated by a comparison between an incoming sound and the memory trace of preceding sounds stored in sensory memory without any attention to the sound. N100 (N1) is associated with the afferent response to sound onset and reflects early analysis of stimulus characteristics. MMN generators are present in the temporal and frontal lobe, and N1 generators are present in the temporal lobe. The parietal lobe is involved in MMN generation elicited by a change in duration. The anatomical network connecting these areas, lateralization, and the effect of the side of ear stimulation on MMN remain unknown. Thus, we studied the effects of low-frequency repetitive transcranial magnetic stimulation (rTMS) over the left parietal lobe on MMN and N1 in 10 healthy subjects. Low-frequency rTMS over the left parietal lobe decreased the amplitude of MMN following right ear sound stimulation, but the amplitude was unaffected with left ear sound stimulation. We observed no significant changes in the amplitude of N1 or the latency of MMN or N1. These results suggest that low-frequency rTMS over the left parietal lobe modulates the detection of early auditory changes in duration in healthy subjects. Stimulation that is contralateral to the side of the ear experiencing sound may affect the generation of duration MMN more than ipsilateral stimulation.

Long-term dynamics of somatosensory activity in a stroke model of distal middle cerebral artery oclussion

A constant challenge in experimental stroke is the use of appropriate tests to identify signs of recovery and adverse effects linked to a particular therapy. In this study, we used a long-term longitudinal approach to examine the functional brain changes associated with cortical infarction in a mouse model induced by permanent ligation of the middle cerebral artery (MCA). Sensorimotor function and somatosensory cortical activity were evaluated with fault-foot and forelimb asymmetry tests in combination with somatosensory evoked potentials. The stroke mice exhibited both long-term deficits in the functional tests and impaired responses in the infarcted and intact hemispheres after contralateral and ipsilateral forepaw stimulation. In the infarcted hemisphere, reductions in the amplitudes of evoked responses were detected after contralateral and ipsilateral stimulation. In the intact hemisphere, and similar to cortical stroke patients, a gradual hyperexcitability was observed after contralateral stimulation but no parallel evidence of a response was detected after ipsilateral stimulation. Our results suggest the existence of profound and persistent changes in the somatosensory cortex in this specific mouse cortical stroke model. The study of evoked potentials constitutes a feasible and excellent tool for evaluating the fitness of the somatosensory cortex in relation to functional recovery after preclinical therapeutic intervention.

Subcortical functional reorganization due to early blindness

Lack of visual input early in life results in occipital cortical responses to auditory and tactile stimuli. However, it remains unclear whether cross-modal plasticity also occurs in subcortical pathways. With the use of functional magnetic resonance imaging, auditory responses were compared across individuals with congenital anophthalmia (absence of eyes), those with early onset (in the first few years of life) blindness, and normally sighted individuals. We find that the superior colliculus, a “visual” subcortical structure, is recruited by the auditory system in congenital and early onset blindness. Additionally, auditory subcortical responses to monaural stimuli were altered as a result of blindness. Specifically, responses in the auditory thalamus were equally strong to contralateral and ipsilateral stimulation in both groups of blind subjects, whereas sighted controls showed stronger responses to contralateral stimulation. These findings suggest that early blindness results in substantial reorganization of subcortical auditory responses.