|
Visual cortex activity in the blind has been shown in sensory tasks. Can it be activated in memory tasks? If so, are
inherent features of its organization meaningfully employed? Our recent results in short-term blindfolded subjects
imply that human primary visual cortex (V1) may operate as a modality-independent 'sketchpad' for working
memory (Likova, 2010a). Interestingly, the spread of the V1 activation approximately corresponded to the spatial
extent of the images in terms of their angle of projection to the subject. We now raise the questions of whether under
long-term visual deprivation V1 is also employed in non-visual memory task, in particular in congenitally blind
individuals, who have never had visual stimulation to guide the development of the visual area organization, and
whether such spatial organization is still valid for the same paradigm that was used in blindfolded individuals. The
outcome has implications for an emerging reconceptualization of the principles of brain architecture and its
reorganization under sensory deprivation. Methods: We used a novel fMRI drawing paradigm in congenitally and
late-onset blind, compared with sighted and blindfolded subjects in three conditions of 20s duration, separated by
20s rest-intervals, (i) Tactile Exploration: raised-line images explored and memorized; (ii) Tactile Memory Drawing:
drawing the explored image from memory; (iii) Scribble: mindless drawing movements with no memory component.
Results and Conclusions: V1 was strongly activated for Tactile Memory Drawing and Tactile Exploration in these
totally blind subjects. Remarkably, after training, even in the memory task, the mapping of V1 activation largely
corresponded to the angular projection of the tactile stimuli relative to the ego-center (i.e., the effective visual angle
at the head); beyond this projective boundary, peripheral V1 signals were dramatically reduced or even suppressed.
The matching extent of the activation in the congenitally blind rules out vision-based explanatory mechanisms, and
supports the more radical idea of V1 as a modality-independent 'projection screen' or a 'sketchpad', whose mapping
scales to the projective dimensions of objects explored in the peri-personal space.
|
