Whole brain functional connectivity in the early blind

Abstract

Early visual deprivation can lead to changes in the brain, which may be explained by either of two hypotheses. The general loss hypothesis has been proposed to explain maladjustments, while the compensatory plasticity hypothesis may explain a superior ability in the use of the remaining senses. Most previous task-based functional MRI (fMRI) studies have supported the compensatory plasticity hypothesis, but it has been difficult to provide evidence to support the general loss hypothesis, since the blind cannot execute visual tasks. The study of resting state fMRI data may provide an opportunity to simultaneously detect the two aspects of changes in the blind. In this study, using a whole brain perspective, we investigated the decreased and increased functional connectivities in the early blind using resting state fMRI data. The altered functional connectivities were identified by comparing the correlation coefficients of each pair of brain regions of 16 early blind subjects (9 males; age range: 15.6-29.3 years, mean age: 22.1 years) with the corresponding coefficients of gender- and age-matched sighted volunteers. Compared with the sighted subjects, the blind demonstrated the decreased functional connectivities within the occipital visual cortices as well as between the occipital visual cortices and the parietal somatosensory, frontal motor and temporal multisensory cortices. Such differences may support the general loss hypothesis. However, we also found that the introduction of Braille earlier in life and for longer daily practice times produced stronger functional connectivities between these brain areas. These findings may support the compensatory plasticity hypothesis. Additionally, we found several increased functional connectivities between the occipital cortices and frontal language cortices in those with early onset of blindness, which indicate the predominance of compensatory plasticity. Our findings indicate that changes in the functional connectivities in the resting state may be an integrated reflection of general loss and compensatory plasticity when a single sensory modality is deprived.

Corticocortical Connections Mediate Primary Visual Cortex Responses to Auditory Stimulation in the Blind

“…A finding that initially seems at odds with our data is that Liu et al (2007) and Yu et al (2008) reported decreased functional connectivity [i.e., correlations of the BOLD signal between brain regions (Friston et al, 1993)] in blind volunteers compared with controls between visual and auditory cortical areas during resting-state fMRI. However, if one considers that the visual cortex can also be activated by auditory stimuli in sighted if the task requires high levels of attention (Cate et al, 2009), the results seem more alike: possibly, the visual cortex of blind people is predominantly recruited during demanding tasks or when relevant information is supplied (Röder et al, 1996).…”

“…However, if one considers that the visual cortex can also be activated by auditory stimuli in sighted if the task requires high levels of attention (Cate et al, 2009), the results seem more alike: possibly, the visual cortex of blind people is predominantly recruited during demanding tasks or when relevant information is supplied (Röder et al, 1996). This would explain why resting-state studies (no attentional demands) failed to find coupling (Liu et al, 2007;Yu et al, 2008), whereas activation-based effective-connectivity studies did find enhanced coupling in the blind (Fujii et al, 2009;present study). This hypothesis is also backed by studies that found attentional modulations of visual cortex activity in the blind (Liotti et al, 1998;Stevens et al, 2007).…”

“…Additional evidence for corticocortical connectivity from auditory to visual cortex comes from activation-based fMRI studies in both sighted (den Ouden et al, 2009;Werner and Noppeney, 2010) and blind humans (Fujii et al, 2009). Support for thalamocortical connections in the blind comes from a resting-state fMRI study (Liu et al, 2007), but a degeneration of the lateral geniculate nucleus (LGN) has also been observed in the blind (Noppeney et al, 2005). Hence, corticocortical connections seem more probable than thalamocortical connections to be mediating auditory responses in the visual cortex of the blind.…”

Thick Visual Cortex in the Early Blind

“…Thus the interruption of synaptic elimination by early visual deprivation may prevent the visual cortex from thinning. Plastic changes have been reported in the visual cortex in resting state (Liu et al, 2007) and imaginary, tactile, and auditory tasks (Noppeney, 2007;Cattaneo et al, 2008), and in the early sensory areas of spared modalities following visual deprivation in early life (Bavelier and Neville, 2002). Thus, plasticity may lead to changes in cortical thickness in the early blind.…”

Rapid Eye Movements (REMs) and visual dream recall in both congenitally blind and sighted subjects

“…While congenitally blind subjects exhibit lower cortical volume in both frontal areas (BA 44, 45) and visual areas (BA 17,18) 48 , compared to a control population, functional connectivity between frontal areas (parts of BA 44, 45, and 47) and occipital areas is stronger in early blind 49 .…”