Glucose utilization in human visual cortex is abnormally elevated in blindness of early onset but decreased in blindness of late onset

Glucose utilization has been studied in the visual cortex of blind human subjects, by comparison with normal volunteers, using positron emission tomography. In 6 subjects who became blind early in life ('early blindness'), metabolism in visual cortex was elevated, comparable to that of normal subjects studied with the eyes open. By contrast, glucose utilization in visual areas of 6 human subjects who became blind after completion of visual development ('late blindness') was decreased, slightly lower than in normal volunteers studied with the eyes closed. This unexpected difference between early and late blind subjects might reflect the persistence, in early blindness, of supranumerary synapses which would escape the normal developmental decrease in synaptic density during infancy

Auditory substitution of vision: pattern recognition by the blind

Pattern recognition in a computer environment was investigated in 6 early blind and 6 blindfolded sighted subjects using auditory substitution of vision. Subjects had to scan visual patterns displayed on a PC screen by moving the pen of a graphics tablet,which lead to corresponding displacements of the cursor on the screen. A small screen area centered on the pointer was then translated into sounds according to a visual-auditory transcription code. Subjects were trained to learn this code during 12 one-hour sessions. Performance of both groups signi®cantly increased with practice. This indicates that mental representations of visual patterns can be acquired through the auditory channel,even in the absence of visual experience. Moreover,blind subjects performed signi®cantly better than sighted subjects did. This could be interpreted as a result of partial compensation for their loss of vision. Pattern recognition in a computer environment is thus possible using a fairly natural visionto-audition coding scheme. Copyright # 2001 John Wiley & Sons,Ltd

The microsystems based visual prosthesis for optic nerve stimulation.

The microsystems based visual prosthesis (MiViP) visual prosthesis generates visual perceptions well below safety and stimulator saturation limits. These perceptions, called phosphenes, are of reasonably small size and are broadly distributed in the visual field. They can thus be used to convey useful visual information. Psychophysical evaluations are being performed in order to assess the implantee's benefits in the use of the MiViP optic nerve visual prosthesis. In a pattern-recognition task, the performance improved regularly with practice with an increasing score and a decreasing delay to recognition. These observations open the way toward an evaluation of general mobility improvement with the portable system. In conclusion, the results obtained so far still support the potential usefulness of the optic nerve visual prosthesis. A low-resolution artificial vision can be expected from the prosthesis after extensive training

High metabolic activity in the visual cortex of early blind human subjects.

Glucose metabolism has been studied in the visual cortex of early blind human subjects. In the forebrain of these subjects, regional glucose utilization was the highest in the striate and prestriate cortical areas. Furthermore, this activity was higher than in blindfolded sighted subjects, whether at rest or during an auditory or tactile task. These observations raise the question of the functionality of the blind's visual cortex

Visual sensations produced by optic nerve stimulation using an implanted self-sizing spiral cuff electrode.

A blind volunteer with retinitis pigmentosa was chronically implanted with a self-sizing spiral cuff electrode around an optic nerve. Electrical stimuli applied to the nerve produced localized visual sensations that were broadly distributed throughout the visual field and could be varied by changing the stimulating conditions. These results demonstrate the potential for constructing a visual prosthesis, based on electrical stimulation of the optic nerve, for blind subjects who have intact retinal ganglion cells