Grazia Fernanda Spitoni

Identification of the neural sources of the pattern-reversal VEP

This study aimed to characterize the neural generators of the early components of the visual-evoked potential (VEP) to pattern-reversal gratings. Multichannel scalp recordings of VEPs and dipole modeling techniques were combined with functional magnetic resonance imaging (fMRI) and retinotopic mapping in order to estimate the locations of the cortical sources giving rise to VEP components in the first 200 ms poststimulus. Dipole locations were seeded to visual cortical areas in which fMRI activations were elicited by the same stimuli. The results provide strong evidence that the first major component of the VEP elicited by a pattern-reversal stimulus (N75/P85) arises from surface-negative activity in the primary visual cortex (area V1). Subsequent waveform components could be accounted for by dipoles that were in close proximity to fMRI activations in the following cortical areas: P95 (area MT/V5), P125/N135 (area V1), N150 (transverse parietal sulcus, TPS), N160 (ventral occipital areas VP, V4v, and V4/V8), and N180 (dorsal occipital areas V3A/V7). These results provide a detailed spatiotemporal profile of the cortical origins of the pattern-reversal VEP, which should enhance its utility in both clinical and basic studies of visual-perceptual processing.

Spatiotemporal analysis of the cortical sources of the steady-state visual evoked potential

This study aimed to characterize the neural generators of the steady‐state visual evoked potential (SSVEP) to repetitive, 6 Hz pattern‐reversal stimulation. Multichannel scalp recordings of SSVEPs and dipole modeling techniques were combined with functional magnetic resonance imaging (fMRI) and retinotopic mapping in order to estimate the locations of the cortical sources giving rise to the SSVEP elicited by pattern reversal. The time‐varying SSVEP scalp topography indicated contributions from two major cortical sources, which were localized in the medial occipital and mid‐temporal regions of the contralateral hemisphere. Colocalization of dipole locations with fMRI activation sites indicated that these two major sources of the SSVEP were located in primary visual cortex (V1) and in the motion sensitive (MT/V5) areas, respectively. Minor contributions from mid‐occipital (V3A) and ventral occipital (V4/V8) areas were also considered. Comparison of SSVEP phase information with timing information collected in a previous transient VEP study (Di Russo et al. [ 2005 ] Neuroimage 24:874–886) suggested that the sequence of cortical activation is similar for steady‐state and transient stimulation. These results provide a detailed spatiotemporal profile of the cortical origins of the SSVEP, which should enhance its use as an efficient clinical tool for evaluating visual‐cortical dysfunction as well as an investigative probe of the cortical mechanisms of visual‐perceptual processing. Hum. Brain Mapp, 2007.

Separate neural systems for processing action- or non-action-related sounds

The finding of a multisensory representation of actions in a premotor area of the monkey brain suggests that similar multimodal action-matching mechanisms may also be present in humans. Based on the existence of an audiovisual mirror system, we investigated whether sounds referring to actions that can be performed by the perceiver underlie different processing in the human brain. We recorded multichannel ERPs in a visuoauditory version of the repetition suppression paradigm to study the time course and the locus of the semantic processing of action-related sounds. Results show that the left posterior superior temporal and premotor areas are selectively modulated by action-related sounds; in contrast, the temporal pole is bilaterally modulated by non-action-related sounds. The present data, which support the hypothesis of distinctive action sound processing, may contribute to recent theories about the evolution of human language from a mirror system precursor.

Spatiotemporal brain mapping of spatial attention effects on pattern-reversal ERPs.

Recordings of event‐related potentials (ERPs) were combined with structural and functional magnetic resonance imaging (fMRI) to investigate the timing and localization of stimulus selection processes during visual‐spatial attention to pattern‐reversing gratings. Pattern reversals were presented in random order to the left and right visual fields at a rapid rate, while subjects attended to the reversals in one field at a time. On separate runs, stimuli were presented in the upper and lower visual quadrants. The earliest ERP component (C1, peaking at around 80 ms), which inverted in polarity for upper versus lower field stimuli and was localized in or near visual area V1, was not modulated by attention. In the latency range 80–250 ms, multiple components were elicited that were increased in amplitude by attention and were colocalized with fMRI activations in specific visual cortical areas. The principal anatomical sources of these attention‐sensitive components were localized by fMRI‐seeded dipole modeling as follows: P1 (ca. 100 ms—source in motion‐sensitive area MT+), C2 (ca. 130 ms—same source as C1), N1a (ca. 145 ms—source in horizontal intraparietal sulcus), N1b (ca. 165 ms—source in fusiform gyrus, area V4/V8), N1c (ca. 180 ms—source in posterior intraparietal sulcus, area V3A), and P2 (ca. 220 ms—multiple sources, including parieto‐occipital sulcus, area V6). These results support the hypothesis that spatial attention acts to amplify both feed‐forward and feedback signals in multiple visual areas of both the dorsal and ventral streams of processing. Hum Brain Mapp, 2011.

Modulation of spontaneous alpha brain rhythms using low-intensity transcranial direct-current stimulation.

Transcranial direct-current stimulation (tDCS) is a form of neurostimulation in which a constant, low current is delivered directly to the brain area of interest by small electrodes. The overall aim of this study was to examine and monitor the modulation of brain activity by electroencephalogram (EEG) in the frequency domain during tDCS in the resting state. To this end, we considered the modulation of spontaneous EEG to be a marker of the perturbation that was induced through the direct current (1.5 mA for 15 min). In all conditions (anodal, cathodal, and sham), an active electrode was placed over the right posterior parietal cortex, and a reference electrode was placed on the ipsilateral deltoid muscle. The EEG was recorded using a 64-channel system. The effect of tDCS was limited to the alpha rhythm, and the anodal stimulation significantly affected the alpha rhythm, whereas the cathodal stimulation did not elicit any modifications. Further, we observed modulation of alpha activity in areas that were stimulated directly through tDCS and in anterior noncontiguous areas. Finally, the anodal effect peaked 7.5 min after stimulation and decreased gradually over time. Our study demonstrates that in the resting brain, monocephalic anodal tDCS over posterior parietal areas alters ongoing brain activity, specifically in the alpha band rhythm. Our data can be used to fine-tune tDCS protocols in neurorehabilitation settings.

Two forms of touch perception in the human brain.

We compared the judgment of distance between two simultaneous tactile stimuli applied to different body parts, with judgment of intensity of skin contact of the very same stimulation. Results on normal subjects showed that both tasks bilaterally activate parietal and frontal areas. However, the evaluation of distances on the body surface selectively activated the angular gyrus and the temporo-parieto-occipital junction in the right hemisphere. The different involvement of the brain areas in the two tactile tasks is interpreted as the need for using a Mental Body Representation (MBR) in the distance task, while the judgment of the intensity of skin deflection can be performed without the mediation of the MBR. The present study suggests that the cognitive processes underlying the two tasks are supported by partially different brain networks. In particular, our results show that metric spatial evaluation is lateralized to the right hemisphere.

Right but not left angular gyrus modulates the metric component of the mental body representation: a tDCS study

The parietal lobes contribute to body-space representation. The present work aims at characterizing the functional role of the inferior parietal lobe in body-space representation and at studying the different roles of the angular gyrus in the right and left hemisphere. We conducted three separate transcranial direct current stimulation (tDCS) experiments using “tactile distance task” as an implicit measure of body representation. Whereas anodal tDCS on the right angular gyrus influences vocal reaction times (vRT) for stimuli delivered on the ipsilateral body parts without changes of accuracy, right tDCS improved both vRT and accuracy for tactile stimuli on the contralateral limbs. Sham or left parietal anodal tDCS had no effect. These evidences support the view that right parietal areas have a crucial role in the metric component of the body representation.

The two dimensions of the body representation in women suffering from Anorexia Nervosa.

A core symptom of Anorexia Nervosa (AN) is a severe alteration of body representations. Evidence from somatoperception studies point to a generic disturbances of somatosensory components of body representations. Here we have investigated whether AN patients (N=18) and controls differed in the perception of tactile stimuli differently oriented along the body axes. We tested the hypothesis that patients perceive and represent their body selectively larger in only one dimension. To this aim we used elementary tactile measures for tactile acuity (Von Freys test and two-point discrimination thresholds - 2PD) and tactile discrimination measures. The rationale is based on the assumption that AN patients have a wider body representation, and that tactile body representation tasks (Tactile Distance task) oriented across the bodies (horizontally) are influenced by distorted body representations compared with tactile stimuli oriented along the bodies (vertically) which should not be influenced by body representations. Results showed that patients judged horizontal tactile stimuli significantly wider than the same stimuli oriented vertically.These results suggest that human brain perceives things differently based on body representations and that the beliefs concerning body size influence the specific somatosensory process of tactile experience.

Sensory-Motor Rehabilitation in Rett Syndrome: A Case Report.

Rett syndrome (RS) is a severe neurodevelopmental disorder that mostly affects females. It is characterized by a regression of motor, cognitive, linguistic, and social abilities and by an inappropriate and stereotypical use of the hands. The purpose of the current study was to explore the possibility of rehabilitating purposeful use of the hands and hand-eye coordination in individuals with this syndrome. G.P., a child affected by RS, received experimental, computerized visual-motor coordination training and a sensory-motor rehabilitative program specifically designed for her based on Piagets (1937) theory of cognitive development. After 3 years of therapy, G.P. partially regained the use of her hands as an instrument of object knowledge and as a means of communicating with people.

Caloric Vestibular Stimulation Reduces Pain and Somatoparaphrenia in a Severe Chronic Central Post-Stroke Pain Patient: A Case Study.

Central post-stroke pain is a neuropathic syndrome characterized by intolerable contralesional pain and, in rare cases, somatic delusions. To date, there is limited evidence for the effective treatments of this disease. Here we used caloric vestibular stimulation to reduce pain and somatoparaphrenia in a 57-year-old woman suffering from central post-stroke pain. Resting-state functional magnetic resonance imaging was used to assess the neurological effects of this treatment. Following vestibular stimulation we observed impressive improvements in motor skills, pain, and somatic delusions. In the functional connectivity study before the vestibular stimulation, we observed differences in the patient’s left thalamus functional connectivity, with respect to the thalamus connectivity of a control group (N = 20), in the bilateral cingulate cortex and left insula. After the caloric stimulation, the left thalamus functional connectivity with these regions, which are known to be involved in the cortical response to pain, disappeared as in the control group. The beneficial use of vestibular stimulation in the reduction of pain and somatic delusion in a CPSP patient is now documented by behavioral and imaging data. This evidence can be applied to theoretical models of pain and body delusions.