حافظه کاری (WM) برای بسامد های Vibrotactile و مقایسه فعالیت قشری در افراد کور و بینا

ABSTRACT Working memory for vibrotactile frequencies: Comparison of cortical activity in blind and sighted individuals

In congenital/early blind (EB), nonvisual stimulation activates all parts of occipital cortex that have been identified with visual stimulation in normally sighted (NS) [Grill-Spector and Malach, 2004; Tootell et al., 1996; Van Essen, 2004]. In NS, striate and immediately adjoining extrastriate cortex normally show minimal cross-modal responsiveness except possibly during visual imagery of nonvisual stimuli. In contrast, several extrastriate areas are multisensory and provide supramodal, abstracted information regardless of input modality [Cattaneo et al., 2008; Pietrini et al., 2004]. In EB, tactile stimulation evokes responses in striate, extrastriate, and larger responses in multisensory extrastriate areas [Burton et al., 2004, 2006]. The cross-modal activation in striate and lower tier extrastriate areas in blindness suggests functional reorganization [Burton, 2003; Burton and McLaren, 2008; Pascual-Leone et al., 2005]; activity in multisensory extrastriate areas might indicate supramodal functions in the blind. However, a role for any occipital cortex activity in EB remains unclear despite evidence of a contribution to Braille literacy [Cohen et al., 1997, 1999; Hamilton et al., 2000].

One possibility is that occipital cortex activity in EB supports behavioral adaptations to blindness. For example, EB particularly rely on memory and augmented retention of verbal descriptions [Amedi et al., 2003], which results in adept serial recall of word lists [Raz et al., 2007]. These long-term verbal recognition processes activate greater positive correlations between response magnitudes in left striate cortex and verbal recognition performance compared to verb generation [Amedi et al., 2003; Raz et al., 2005]. Furthermore, preferential left occipital cortex activation in verbal semantic and recognition tasks parallels left dominance for language in frontal cortex [Amedi et al., 2003].

Equally important for EB is short-term working memory (WM) of tactile and auditory sensations when navigating the environment. In NS people, WM for visualized environments is crucial in spatial localization. Similarly, EB use spatial WM for touched objects to develop mental images of space [Vecchi, 1998; Vecchi et al., 2004] and spatial parameters of configuration and orientation of these objects. In EB, a tactile version of a spatial WM task activated the same dorsal extrastriate ‘‘visual’’ areas [Bonino et al., 2008] engaged in NS with similar spatial tactile and visual WM paradigms [Ricciardi et al., 2006]. Thus, EB tend to show utilization of the same ‘‘where’’ networks in the dorsal ‘‘visual’’ system for spatial WM engaged by sighted.

A primary aim of the present study was to determine whether a WM task involving tactile vibration stimulation selectively activated any occipital areas in EB. To disambiguate the study of WM processes, the current paradigm was nonverbal, stimuli were unidimensional, and required no tactile spatial processing. Furthermore, no haptic behavior was required because stimulation was passive with completely controlled parameters. A key control was using identical stimulation parameters for the WM and sensory detection tasks. Consequently, activation of striate cortex in EB during a bare essential task may elucidate the role of this cortex in tactile WM. Furthermore, results in multisensory extrastriate areas examine whether a simple tactile WM task is similarly processed by EB and NS in supramodal regions. The issue in extrastriate multisensory areas is whether a simple tactile WM task is sufficient to activate these regions.

A secondary goal was to ascertain whether prefrontal and parietal region contributions to WM and attention to memory (reviewed in Barch and Smith [2008], Cabeza and Nyberg [2000], Curtis and D’Esposito [2003], Duncan and Owen [2000], Jonides et al. [2008], and Wager and Smith [2003]) differed in EB compared to NS. We also examined sensory processing of tactile vibrations in somatosensory and premotor areas for possible group differences. Analyses in these different regions sought to determine whether known superior attention performance in EB [Collignon et al., 2006] might explain activity differences between groups. Better attentional performance in EB could account for better recall of tactile objects [D’Angiulli and Waraich, 2002], which might find neurophysiological expression in response differences in attention and somatosensory areas.