In man and monkey, absolute cortical blindness is caused by destruction of the optic radiations and/or the primary visual cortex. It is characterized by an absence of any conscious vision, but stimuli presented inside its borders may nevertheless be processed. This unconscious vision includes neuroendocrine, reflexive, indirect and forced-choice responses which are mediated by the visual subsystems that escape the direct cerebral damage and the Ensuring degeneration. While extrastriate cortical areas participate in the mediation of the forced-choice responses, a concomitant striate cortical activation does not seem to be necessary for blindsight. Whether the loss of phenomenal vision is a necessary consequence of striate cortical destruction and whether this structure is indispensable for conscious sight are much debated questions which need to be tackled experimentally.

Patients with lesions in the primary visual cortex (V1) may show processing of visual stimuli presented in their field of cortical blindness even when they report being unaware of the stimuli. To elucidate the neuroanatomical basis of their residual visual functions, we used functional magnetic resonance imaging in two hemianopic patients, FS and GY. In the first experiment, a rotating spiral stimulus was used to assess the responsiveness of dorsal stream areas. Although no response was detectable within denervated or destroyed early visual cortex, motion-sensitive areas (hMT+/V5) ipsilateral to the lesion showed a strong sustained hemodynamic response. In GY, this activation was at least as strong as that of his contralesional hMT+/V5 to the stimulus in the normal hemifield. In the second experiment, coloured images of natural objects were used to assess the responsiveness of ventral stream areas. Again, no activity was detectable in ipsilesional early visual areas, but extrastriate areas in the lateral occipital cortex (hMT+/V5 and LO) and within the posterior fusiform gyrus (V4/V8) showed a robust sustained hemodynamic response. In both experiments, we observed that ipsilesional areas responded to stimuli presented in either hemifield, whereas the normal hemisphere responded preferentially to stimuli in the sighted hemifield. As only one subject occasionally noticed the onset of stimulation in the impaired field, the unexpectedly strong sustained activity in ipsilesional dorsal and ventral cortical areas appears to be insufficient to generate conscious vision.

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Blindsight, the visually evoked voluntary responses of patients with striate cortical destruction that are demonstrated despite a phenomenal blindness, has attracted attention from neuroscientists and philosophers interested in problems of perceptual consciousness and its neuronal basis. It is assumed to be mediated by the numerous extra-geniculostriate cortical retinofugal pathways whose properties are studied primarily in monkeys. Like patients with blindsight, monkeys with lesions of the primary visual cortex can learn to detect, localize and distinguish between visual stimuli presented within their visual field defects. Although the patients deny seeing the stimuli they can nevertheless respond to (by forced-choice guessing) in their phenomenally blind fields, it is not known whether the monkeys experience the same absence of phenomenal vision. To determine whether they too have blindsight, or whether they actually see the stimuli in their field defects, monkeys who showed excellent detection in tasks where a visual stimulus was presented on every trial, albeit at different positions, were tested in a signal-detection task in which half the trials were blank trials, with no visual stimulus. They classified the visual stimuli presented in the field defect as blank trials, demonstrating, like patients, blindsight rather than degraded real vision.

The commonsense view of religious experience is that it is a preconceptual, immediate affective event. Work in philosophy and psychology, however, suggest that religious experience is an attributional cognitive phenomenon. Here the neural correlates of a religious experience are investigated using functional neuroimaging. During religious recitation, self-identified religious subjects activated a frontal-parietal circuit, composed of the dorsolateral prefrontal, dorsomedial frontal and medial parietal cortex. Prior studies indicate that these areas play a profound role in sustaining reflexive evaluation of thought. Thus, religious experience may be a cognitive process which, nonetheless, feels immediate.