Abstract
Visual cortex activity in the blind has been shown in sensory tasks. Can it be activated in memory tasks? 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, 2010). We now raise the question of whether under long-term visual deprivation V1 is also employed in non-visual memory, in particular in congenitally blind subjects, who have never had visual stimulation to guide the development of the visual area organization. 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 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, 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); beyond this projective boundary, peripheral V1 signals were dramatically reduced or 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 an modality-independent “sketchpad” whose mapping scales to the projective dimensions of objects explored in the peripersonal space. In higher occipital areas the differential pattern of engagement across the subject categories suggests progressive neuroplastic reorganization as visual deprivation is prolonged, in accord with an evolving cross-modal utilization of the occipital cortex to maximize its inherent functional potential.
NSF/SLC grant to LLikova.