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We have previously shown that some visual motion areas can be specifically recruited by auditory motion processing in blindfolded sighted subjects [Poirier, C., Collignon, O., De Volder, A.G., Renier, L., Vanlierde, A., Tranduy, D., Scheiber, C., 2005. Specific activation of V5 brain area by auditory motion processing: an fMRI study. Brain Res. Cogn. Brain Res. 25, 650-658]. The present fMRI study investigated whether auditory motion processing may recruit the same brain areas in early blind subjects. The task consisted of simultaneously determining both the nature of a sound stimulus (pure tone or complex sound) and the presence or absence of its movement. When a movement was present, blind subjects had to identify its direction. Auditory motion processing, as compared to static sound processing, activated the brain network of auditory and visual motion processing classically observed in sighted subjects. Accordingly, brain areas previously considered as specific to visual motion processing could be specifically recruited in blind people by motion stimuli presented through the auditory modality. This indicates that the occipital cortex of blind people could be organized in a modular way, as in sighted people. The similarity of these results with those we previously observed in sighted subjects suggests that occipital recruitment in blind people could be mediated by the same anatomical connections as in sighted subjects.

The learning process related to pattern and object recognition is difficult to study because the human brain has a remarkable capacity to recognise complex visual forms from early infancy. In the present study, we investigated on-going neural changes underlying the learning process of visual pattern recognition by means of a device substituting audition for vision. Functional MRI evidenced the gradual pattern recognition-induced recruitment of the ventral visual stream, bilaterally, from learning session 1 to session 3, and a slight decrease in these activation foci from session 3 to session 4. The initial increase in activation is thought to reflect the gradually enhanced visualisation of patterns in the subjects' mind across sessions. By contrast the subsequent decrease reported at the end of the training period is interpreted as the progressive optimisation of neuronal responses elicited by the task. Our results, in accordance with previous observations, suggest that the succession of activation increase and decrease in sensori-motor areas could be a general rule in sensory and sensori-motor learning.

Previous neuroimaging studies identified multimodal brain areas in the visual cortex that are specialized for processing specific information, such as visual-haptic object recognition. Here, we test whether visual brain areas are involved in depth perception when auditory substitution of vision is used. Nine sighted volunteers were trained blindfolded to use a prosthesis substituting vision with audition both to recognize two-dimensional figures and to estimate distance of an object in a real three-dimensional environment. Using positron emission tomography, regional cerebral blood flow was assessed while the prosthesis was used to explore virtual 3D images; subjects focused either on 2D features (target search) or on depth (target distance comparison). Activation foci were found in visual association areas during both the target search task, which recruited the occipito-parietal cortex, and the depth perception task, which recruited occipito-parietal and occipito-temporal areas. This indicates that some brain areas of the visual cortex are relatively multimodal and may be recruited for depth processing via a sense other than vision.

Using functional magnetic resonance imaging, the brain activation related to unilateral sequential finger-to-thumb opposition was studied in six children with a right congenital hemiplegia of cortical origin. They were compared to six age-matched controls. In the control group, movements with either hand asymmetrically activated the sensorimotor cortex and premotor areas in both cerebral hemispheres with a typical contralateral predominance. By contrast, paretic finger movements activated both hemispheres in the hemiplegic patients, with a strong ipsilateral predominance favoring the undamaged hemisphere. The activation induced by nonparetic finger movements was restricted to the contralateral undamaged hemisphere. Furthermore, the level of activation in the undamaged cortex was partly related to residual finger dexterity, according to covariance analysis. These activation patterns indicate an adaptive reorganization of the cortical motor networks in this group of patients, with a prominent involvement of the undamaged hemisphere in the control of finger movements with either hand.

Using positron emission tomography, regional cerebral blood flow was studied in five early blind and five control volunteers during visuo-spatial imagery. Subjects were instructed to generate a mental representation of verbally provided bidimensional patterns that were placed in a grid and to assess pattern symmetry in relation to a grid axis. This condition was contrasted with a verbal memory task. Cerebral activation in both groups was similar during the visuo-spatial imagery task. It involved the precuneus (BA 7), superior parietal lobule (BA 7), and occipital gyrus (BA 19). These results are in accordance with previous studies conducted in sighted subjects that indicated that the same occipito-parietal areas are involved in visual perception as well as in mental imagery dealing with spatial components. The dorsal pathway seems to be involved in visuo-spatial imagery in early blind subjects, indicating that this pathway undergoes development in the absence of vision.

Before the completion of visual development, visual deprivation impairs synaptic elimination in the visual cortex. The purpose of this study was to determine whether the distribution of central benzodiazepine receptor (BZR) is also altered in the visual cortex in subjects with early-onset blindness. Positron emission tomography was carried out with [(15)O]water and [(11)C]flumazenil on six blind subjects and seven sighted controls at rest. We found that the CBF was significantly higher in the visual cortex for the early-onset blind subjects than for the sighted control subjects. However, there was no significant difference in the BZR distribution in the visual cortex for the subject with early-onset blindness than for the sighted control subjects. These results demonstrated that early visual deprivation does not affect the distribution of GABA(A) receptors in the visual cortex with the sensitivity of our measurements. Synaptic elimination may be independent of visual experience in the GABAergic system of the human visual cortex during visual development.

The resting brain metabolism was estimated in six children suffering from a right congenital hemiplegia (CH) of subcortical origin. This estimate was based on the 18F-labeled 2-deoxy-2-fluoro-d-glucose (FDG) uptake measured by means of positron emission tomography and compared, using statistical parametric mapping (SPM99), with that of six control subjects. The contrast [CH children - Controls] showed that CH children had two loci of relatively higher FDG uptake. The larger voxel cluster was found in the ipsilesional hemisphere and comprised the primary motor and somatosensory cortices and left inferior parietal lobule. The other cluster was located in the contralesional hemisphere and encompassed the primary motor cortex, callosomarginal sulcus, and cingulate gyrus. The reverse contrast [Controls - CH children] showed that control subjects had a relatively higher FDG uptake bilaterally in the temporal and hippocampal gyri, the rostral part of the brain stem, the thalami, the putamen, and the superior frontal gyri. A crossed cerebellar diaschisis was not observed in CH children. This relatively higher FDG uptake in the ipsi- and contralesional motor areas of CH children stands out in contrast to the hypometabolism (diaschisis) frequently observed in adult stroke patients with a subcortical lesion. This increased FDG uptake in the disconnected ipsilesional motor areas may reflect a long-term adaptation leading, for example, to an increased synaptic density and/or activity or to a change in the density of glucose transporters., ((C)2002 Elsevier Science (USA).)

Previous neuroimaging studies identified a large network of cortical areas involved in visual imagery in the human brain, which includes occipitotemporal and visual associative areas. Here we test whether the same processes can be elicited by tactile and auditory experiences in subjects who became blind early in life. Using positron emission tomography, regional cerebral blood flow was assessed in six right-handed early blind and six age-matched control volunteers during three conditions: resting state, passive listening to noise sounds, and mental imagery task (imagery of object shape) triggered by the sound of familiar objects. Activation foci were found in occipitotemporal and visual association areas, particularly in the left fusiform gyrus (Brodmann areas 19-37), during mental imagery of shape by both groups. Since shape imagery by early blind subjects does involve similar visual structures as controls at an adult age, it indicates their developmental crossmodal reorganization to allow perceptual representation in the absence of vision.

This PET study aimed at investigating the neural structures involved in pattern recognition in early blind subjects using sensory substitution equipment (SSE). Six early blind and six blindfolded sighted subjects were studied during three auditory processing tasks: a detection task with noise stimuli, a detection task with familiar sounds, and a pattern recognition task using the SSE. The results showed a differential activation pattern with the SSE as a function of the visual experience: in addition to the regions involved in the recognition process in sighted control subjects, occipital areas of early blind subjects were also activated. The occipital activation was more important when the early blind subjects used SSE than during the other auditory tasks. These results suggest that activity of the extrastriate visual cortex of early blind subjects can be modulated and bring additional evidence that early visual deprivation leads to cross-modal cerebral reorganization., (Copyright 2001 Academic Press.)