Category: Research

Month: 31 Oct 2016

Issue: not yet available

Response to visual stimuli in Argus II implanted patients may improve with prolonged use of the device.

Research led by the University of Pisa on patients that had received implantation of the Argus II retinal prosthesis device suggest that neural plasticity in the brain may benefit from prolonged use. The research indicated that in six out of seven retinitis pigmentosa (RP) patients, high contrast stimuli were detected by the patients following surgical implantation while prior to surgery the ability to detect such stimuli were either weak or absent. The researchers suggest that their results support the concept that visual benefit may be restored in patients after years or decades of visual stimulation deprivation in the brain. Increased usage of the device over time appears to strengthen the neural pathways of stimulation however, the number of patients tested was small and the results tentative and subject to larger numbers of patients over an increased duration of time.

 

As there are many therapies currently in development for retinal pathologies, such as optogenetics, gene therapy and artificial prosthetic devices, it may be important to define what factors might optimally benefit patients receiving such novel interventions. Prior research has indicated an incredible plasticity of the brain to accommodate trauma and stimulant deprivation in which either new neural pathways, or increased use of existing ones, attempt to compensate for an upstream fault. In terms of prosthetic devices, two commercially available solutions include a subretinal visual implant (Alpha IMS from Retina Implant AG in Germany), and an epiretinal implant (Argus II from Second Sight in the US). The current study examined a group of seven blind patients (4 male and 3 females) aged 60 ± 6 years), each affected with RP and having only bare light perception, before and after (17 ± 7 month interval) implantation with the Argus II device.

 

The researchers measured the BOLD response (blood oxygenation levels dependent activity) both before and after surgery in response to a sequence of 1Hz light flashes. In three of the patients tested who had complied with the training procedure, activation was found to increase in the V1 region of the brain. In addition, responses in the LGN became statistically significant for the right hemisphere [RH] ipsilateral to the implant, p <0.01, uncorrected). It was not clear if the result is mediated by local retinal mechanisms or by releasing vetoed mechanisms at a central level in the brain, either in the thalamus or cortex. According to the Italian research group, the results demonstrate that “the adult visual brain retains a degree of plasticity and is able to reorganize its response to process new and abnormal incoming inputs after many years of deprivation in adulthood. The boost in BOLD response takes a long time and intensive training to appear, being stronger in those subjects who used the prosthetic device more intensely and for a longer time.”

 

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