The Extrastriate Body Area and identity processing: An fMRI guided TMS study.

The extrastriate body area (EBA) is a body-selective focal region located in the lateral occipito-temporal cortex that responds strongly to images of human bodies and body parts in comparison with other classes of stimuli. Whether EBA contributes also to the body recognition of self versus others remains in debate. We investigated whether EBA contributes to self-other distinction and whether there might be a hemispheric-side specificity to that contribution using double-pulse transcranial magnetic stimulation (TMS) in right-handed participants. Prior to the TMS experiment, all participants underwent an fMRI localizer task to determine individual EBA location. TMS was then applied over either right EBA, left EBA or vertex, while participants performed an identification task in which images of self or others' right, or left hands were presented. TMS over both EBAs slowed responses, with no identity-specific effect. However, TMS applied over right EBA induced significantly more errors on other's hands than noTMS, TMS over left EBA or over the Vertex, when applied at 100-110 ms after image onset. The last three conditions did not differ, nor was there any difference for self-hands. These findings suggest that EBA participates in self/other discrimination.

Interlimb Transfer of Reach Adaptation Does Not Require an Intact Corpus Callosum: Evidence from Patients with Callosal Lesions and Agenesis.

Generalization of sensorimotor adaptation across limbs, known as interlimb transfer, is a well-demonstrated phenomenon in humans, yet the underlying neural mechanisms remain unclear. Theoretical models suggest that interlimb transfer is mediated by interhemispheric transfer of information via the corpus callosum. We thus hypothesized that lesions of the corpus callosum, especially to its midbody connecting motor, supplementary motor, and premotor areas of the two cerebral hemispheres, would impair interlimb transfer of sensorimotor adaptation. To test this hypothesis, we recruited three patients: two rare stroke patients with recent, extensive callosal lesions including the midbody and one patient with complete agenesis. A prismatic adaptation paradigm involving unconstrained arm reaching movements was designed to assess interlimb transfer from the prism-exposed dominant arm (DA) to the unexposed non-dominant arm (NDA) for each participant. Baseline results showed that spatial performance of each patient did not significantly differ from controls, for both limbs. Further, each patient adapted to the prismatic perturbation, with no significant difference in error reduction compared with controls. Crucially, interlimb transfer was found in each patient. The absolute magnitude of each patient's transfer did not significantly differ from controls. These findings show that sensorimotor adaptation can transfer across limbs despite extensive lesions or complete absence of the corpus callosum. Therefore, callosal pathways connecting homologous motor, premotor, and supplementary motor areas are not necessary for interlimb transfer of prismatic reach adaptation. Such interlimb transfer could be mediated by transcallosal splenium pathways (connecting parietal, temporal and visual areas), ipsilateral cortico-spinal pathways or subcortical structures such as the cerebellum.

Brain Regions Associated to a Kinesthetic Illusion Evoked by Watching a Video of One's Own Moving Hand.

It is well known that kinesthetic illusions can be induced by stimulation of several sensory systems (proprioception, touch, vision…). In this study we investigated the cerebral network underlying a kinesthetic illusion induced by visual stimulation by using functional magnetic resonance imaging (fMRI) in humans. Participants were instructed to keep their hand still while watching the video of their own moving hand (Self Hand) or that of someone else's moving hand (Other Hand). In the Self Hand condition they experienced an illusory sensation that their hand was moving whereas the Other Hand condition did not induce any kinesthetic illusion. The contrast between the Self Hand and Other Hand conditions showed significant activation in the left dorsal and ventral premotor cortices, in the left Superior and Inferior Parietal lobules, at the right Occipito-Temporal junction as well as in bilateral Insula and Putamen. Most strikingly, there was no activation in the primary motor and somatosensory cortices, whilst previous studies have reported significant activation in these regions for vibration-induced kinesthetic illusions. To our knowledge, this is the first study that indicates that humans can experience kinesthetic perception without activation in the primary motor and somatosensory areas. We conclude that under some conditions watching a video of one's own moving hand could lead to activation of a network that is usually involved in processing copies of efference, thus leading to the illusory perception that the real hand is indeed moving.

Benefits of computer-based memory and attention training in healthy older adults.

Multifactorial cognitive training programs have a positive effect on cognition in healthy older adults. Among the age-sensitive cognitive domains, episodic memory is the most affected. In the present study, we evaluated the benefits on episodic memory of a computer-based memory and attention training. We targeted consciously controlled processes at encoding and minimizing processing at retrieval, by using more familiarity than recollection during recognition. Such an approach emphasizes processing at encoding and prevents subjects from reinforcing their own errors. Results showed that the training improved recognition performances and induced near transfer to recall. The largest benefits, however, were for tasks with high mental load. Improvement in free recall depended on the modality to recall; semantic recall was improved but not spatial recall. In addition, a far transfer was also observed with better memory self-perception and self-esteem of the participants. Finally, at 6-month follow up, maintenance of benefits was observed only for semantic free recall. The challenge now is to corroborate far transfer by objective measures of everyday life executive functioning.

Lateral occipitotemporal cortex and action representation.

Representation of body and body movements is essential for identifying others intentions or actions or for learning from them. Over the last 10 years, a large collection of research has demonstrated that body representations are distributed across a widely distributed brain network. In this functional magnetic resonance imaging study, we focus on lateral occipitotemporal cortex (LOTC), a recently identified brain region that could represent the body in a multisensory and dynamic manner. We addressed the question of LOTC involvement in visual processing of others׳ actions through a factorial analysis that manipulated the meaning of an observed action, completed by a psychophysiological interaction analysis. The results show that only left LOTC was significantly activated in relation to others׳ actions meaning. In addition, only left LOTC was activated during both action observation and action production but it was more dorsal than the activation related to the meaning of observed actions. Furthermore, the psychophysiological interaction analysis showed that when watching meaningless actions, the more dorsal part of the LOTC (the area active during both action production and action observation) had higher functional connectivity with primary visual areas while the more ventral part (that responded to action meaning) had higher correlation with anterior cingulate and medioprefrontal cortices. Taken together these results plead in favour of a strong implication of left LOTC in action observation and understanding, with a possible functional specialisation between the more ventral and the more dorsal parts of LOTC.

Where is your shoulder? Neural correlates of localizing others' body parts.

Neuropsychological studies, based on pointing to body parts paradigms, suggest that left posterior parietal lobe is involved in the visual processing of other persons' bodies. In addition, some patients have been found with mild deficit when dealing with abstract human representations but marked impairment with realistically represented bodies, suggesting that this processing could be modulated by the abstraction level of the body to be analyzed. These issues were examined in the present fMRI experiment, designed to evaluate the effects of visually processing human bodies of different abstraction levels on brain activity. The human specificity of the studied processes was assessed using whole-body representations of humans and of dogs, while the effects of the abstraction level of the representation were assessed using drawings, photographs, and videos. To assess the effect of species and stimulus complexity on BOLD signal, we performed a two-way ANOVA with factors species (human versus animal) and stimulus complexity (drawings, photographs and videos). When pointing to body parts irrespective of the stimulus complexity, we observed a positive effect of humans upon animals in the left angular gyrus (BA 39), as suggested by lesion studies. This effect was also present in midline cortical structures including mesial prefrontal, anterior cingulate and precuneal regions. When pointing to body parts irrespective of the species to be processed, we observed a positive effect of videos upon photographs and drawings in the right superior parietal lobule (BA 7), and bilaterally in the superior temporal sulcus, the supramarginal gyrus (BA 40) and the lateral extrastriate visual cortex (including the "extrastriate body area"). Taken together, these data suggest that, in comparison with other mammalians, the visual processing of other humans' bodies is associated with left angular gyrus activity, but also with midline structures commonly implicated in self-reference. They also suggest a role of the lateral extrastriate cortex in the processing of dynamic and biologically relevant body representations.

A new vibrator to stimulate muscle proprioceptors in fMRI.

Studying cognitive brain functions by functional magnetic resonance imaging (fMRI) requires appropriate stimulation devices that do not interfere with the magnetic fields. Since the emergence of fMRI in the 90s, a number of stimulation devices have been developed for the visual and auditory modalities. Only few devices, however, have been developed for the somesthesic modality. Here, we present a vibration device for studying somesthesia that is compatible with high magnetic field environments and that can be used in fMRI machines. This device consists of a poly vinyl chloride (PVC) vibrator containing a wind turbine and of a pneumatic apparatus that controls 1-6 vibrators simultaneously. Just like classical electromagnetic vibrators, our device stimulates muscle mechanoreceptors (muscle spindles) and generates reliable illusions of movement. We provide the fMRI compatibility data (phantom test), the calibration curve (vibration frequency as a function of air flow), as well as the results of a kinesthetic test (perceived speed of the illusory movement as a function of vibration frequency). This device was used successfully in several brain imaging studies using both fMRI and magnetoencephalography.

Relationship between the velocity of illusory hand movement and strength of MEG signals in human primary motor cortex and left angular gyrus.

We studied the relationship between the velocity of movement illusion and the activity level of primary motor area (M1) and of the left angular gyrus (AG) in humans. To induce illusory movement perception, we applied co-vibration at different frequencies on tendons of antagonistic muscle groups. Since it is well established that the velocity of illusory movement is related to the difference in vibration frequency applied to two antagonistic muscles, we compared magnetoencephalography (MEG) signals recorded in two conditions of co-vibration: in the "fast illusion" condition a frequency difference of 80 Hz was applied on the tendons of the right wrist extensor and flexor muscle groups, whereas in the "slow illusion" condition a frequency difference of 40 Hz was applied on the same muscle groups. The dipole strength, reflecting the activity level of structures, was measured over M1 and the left AG in two different time-periods: 0-400 and 400-800 ms in each condition. Our results showed that the activity level of the AG was similar in both conditions whatever the time-period, whereas the activity level of M1 was higher in the "fast illusion" condition compared to the "slow illusion" condition from 400 ms after the vibration onset only. The data suggest that the two structures differently contributed to the perception of illusory movements. Our hypothesis is that M1 would be involved in the coding of cinematic parameters of the illusory movement but not the AG.

Cortical correlates of illusory hand movement perception in humans: a MEG study.

The present study aimed to investigate cortical activity associated with perception of illusory hand movements elicited by tendon vibration using magnetoencephalography (MEG) in humans. We compared MEG responses in two conditions of stimulation, "illusion" and "no illusion". In the "illusion" condition, covibration at different frequencies applied on the tendons of the right wrist flexor and extensor muscle groups evoked illusory movements of the hand. In the "no illusion" condition, covibration was delivered at the same frequency on both tendon groups and no movement was perceived. In both experimental conditions, equivalent current dipoles (ECD) were identified in each of four time windows: 0-200 ms, 200-400 ms, 400-600 ms and 600-800 ms. Our data showed similar activation in S1, superior parietal gyrus and supramarginal gyrus in both conditions, whereas the supplementary motor area, M1 and the left angular gyrus were found active in the "illusion" condition only. Our results confirmed the role of posterior parietal areas as well as motor areas in the arising of kinesthetic sensations. The hypothesis of an interaction between the angular gyrus and the primary motor area occurring about 400 ms after the beginning of the stimulation is discussed.

Transcranial magnetic stimulation of the sensorimotor cortex alters kinaesthesia.

Tendon vibration is known to evoke perception of illusory movements, together with motor responses in the muscles antagonistic to those vibrated. In the present study, we assessed the perceptual and motor effects of transcranial magnetic stimulation of the sensorimotor cortex during illusions of hand movements evoked by vibration of wrist muscle tendons. The results showed that transcranial magnetic stimulation could accelerate or decelerate the illusory movements, depending on the site and intensity of magnetic stimulation. Whenever transcranial magnetic stimulation decelerated illusory movements, motor responses decreased, whereas whenever it accelerated illusory movements, motor responses increased. We conclude that motor responses associated with movement illusions have a cortical stage, because they are affected by experimentally induced disruption of activity in intracortical networks.

The role of human left superior parietal lobule in body part localization.

Electrophysiological data in primates suggest that the superior parietal lobule integrates the position of the limbs to construct complex representations of postures. Although in humans the neural basis of these mechanisms remains largely unknown, neuropsychological studies have implicated left superior parietal regions. We devised a simple functional magnetic resonance imaging paradigm aimed at exploring this hypothesis in healthy humans. Strong activation was obtained within the left but not the right superior parietal lobule, providing additional evidence that this structure may play a key role in body part localization processing.

Motor and parietal cortical areas both underlie kinaesthesia.

Tendon vibration has long been known to evoke perception of illusory movements through activation of muscle spindle primary endings. Few studies, however, have dealt with the cortical processes resulting in these kinaesthetic illusions. We conceived an fMRI experiment to investigate the cortical structures taking part in these illusory perceptions. Since muscle spindle afferents project onto different cortical areas involved in motor control it was necessary to discriminate between activation related to sensory processes and activation related to perceptual processes. To this end, we designed and compared different conditions. In two illusion conditions, covibration at different frequencies of the tendons of the right wrist flexor and extensor muscle groups evoked perception of slow or fast illusory movements. In a no illusion condition, covibration at the same frequency of the tendons of these antagonist muscle groups did not evoke a sensation of movement. Results showed activation of most cortical areas involved in sensorimotor control in both illusion conditions. However, in most areas, activation tended to be larger when the movement perceived was faster. In the no illusion condition, motor and premotor areas were little or not activated. Specific contrasts showed that perception of an illusory movement was specifically related to activation in the left premotor, sensorimotor, and parietal cortices as well as in bilateral supplementary motor and cingulate motor areas. We conclude that activation in motor as well as in parietal areas is necessary for a kinaesthetic sensation to arise.