Task-dependent V1 responses in human retinitis pigmentosa

Area of Science:

• Neuroscience
• Visual Neuroscience
• Functional Magnetic Resonance Imaging (fMRI)

Background:

• Individuals with macular degeneration (MD) exhibit a non-responsive lesion projection zone (LPZ) in V1 during passive viewing fMRI.
• fMRI responses can be elicited from the LPZ when subjects engage in stimulus-related tasks.
• Retinitis pigmentosa (RP) is characterized by intact foveal vision but peripheral visual field loss.

Purpose of the Study:

• To investigate fMRI measurements in subjects with retinitis pigmentosa (RP).
• To determine if task engagement influences fMRI responses in the V1 LPZ of RP patients.

Main Methods:

• fMRI was conducted on three RP subjects and two control subjects.
• Subjects viewed drifting contrast pattern stimuli under passive viewing and stimulus-related task conditions.

Main Results:

• In RP subjects, the BOLD response in the posterior calcarine cortex was stimulus-in-phase during passive viewing.
• An anterior LPZ showed opposite-phase responses during passive viewing, indicating a lack of direct retinal input.
• During stimulus-related tasks, LPZ responses in RP subjects modulated in phase with the stimulus and task, unlike controls.

Conclusions:

• Task-dependent LPZ responses in RP subjects resemble those in MD subjects.
• This supports the hypothesis that loss of retinal input to the LPZ unmasks pre-existing extrastriate feedback signals.
• Findings have implications for visual therapy aimed at restoring vision by replacing missing V1 LPZ inputs.