Multisensory cortical integration in patients with hereditary cone dystrophy: a fMRI and DTI study

Hereditary cone dystrophies (HCD) determine deprivation of normal visual input to the portion of V1 representing the macula. In congenitally blind subjects, Functional MRI studies (fMRI) demonstrated that the “deafferented” V1 responds to stimuli of different sensory modalities. We aim to understand if a similar reorganization is present in HCD. In 7 HCD patients and 7 normal subjects we measured fMRI cortical response to audio, visual and audio-visual stimuli and used MR Diffusion Tensor Imaging (DTI) to quantify the integrity of the optic radiations and the connections between V1 and A1. The ON stimuli were expanding-contracting visual flow motion (extending 3 deg within the scotoma), auditory looming-receding flow motion, or a combination of the two. The OFF stimulus was a grey background with peripheral square stimulus to help fixation. Although in normal blind folded subjects no response to sound was ever observed in V1/V2, in HCD patients acoustic stimuli activated deafferented V1. DTI results revealed no differences in white matter microstructure between patients and controls along the Inferior Longitudinal Fasciculus or the Inferior fronto-occipital fasciculus. This data suggests a cortical reorganization of function in deafferented V1, despite the late onset of the disease and the lack of major anatomical changes.