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Visual evoked magnetic fields to flash and pattern in 100 normal subjects.
R A Armstrong1, A Slaven, G F Harding
1Department of Vision Sciences, Aston University, Birmingham, England.
Vision Research
|January 1, 1991
Summary
This study explored recording visual evoked magnetic fields in 100 individuals. The pattern reversal response (P100M) showed age-related latency increases after 55 years, unlike flash responses (P2M).
Area of Science:
- Biophysics
- Neuroscience
- Ophthalmology
Background:
- Visual evoked magnetic fields (VEMFs) offer a non-invasive method to assess visual pathway function.
- Previous studies have focused on shielded environments, limiting real-world applicability.
- Understanding age-related changes in VEMFs is crucial for diagnosing visual processing disorders.
Purpose of the Study:
- To investigate the feasibility of recording VEMFs in an unshielded environment.
- To establish latency norms for pattern reversal (P100M) and flash (P2M) VEMF components.
- To analyze the impact of aging on VEMF latencies.
Main Methods:
- Recording VEMFs using a single-channel d.c. SQUID second-order gradiometer in 100 subjects (15-87 years).
- Stimuli included pattern reversal and flash visual stimuli.
- Analysis focused on the latency of the major positive components: P100M and P2M.
Main Results:
- Practical recording of VEMFs was achieved in an unshielded setting.
- The P100M component (90-120 ms) and P2M component (90-140 ms) were identified.
- P100M latency norms were more variable than visual evoked potentials (VEPs).
- A significant age-related increase in P100M latency was observed after 55 years.
- A less pronounced age trend was noted for P2M latency.
Conclusions:
- VEMF recording is practical in unshielded environments, expanding clinical utility.
- P100M latency demonstrates significant age-related changes, particularly after 55 years.
- VEMFs, especially P100M, show potential as sensitive biomarkers for age-related visual pathway alterations.