Identification of the hemisphere activated by hemifield visual stimulation using a single equivalent dipole model

Area of Science:

• Neuroscience
• Ophthalmology
• Biophysics

Background:

• Pattern visual evoked potential (PVEP) amplitude distribution exhibits significant intersubject variability.
• Hemifield stimulation can lead to paradoxical P100 amplitudes, with larger responses ipsilateral to the stimulated field in some individuals.
• Surface topographic maps of PVEPs are unreliable for determining the stimulated hemifield or activated hemisphere.

Purpose of the Study:

• To evaluate the efficacy of a single equivalent dipole model in identifying the stimulated hemifield despite variable surface amplitude distributions.
• To determine if dipole modeling can accurately identify the activated hemisphere in hemifield PVEP recordings.
• To investigate the relationship between equivalent dipole orientation and surface amplitude topography.

Main Methods:

• Recording hemifield pattern visual evoked potentials (PVEPs) from 14 normal subjects.
• Analyzing the topographic amplitude distribution of the P100 peak.
• Applying a single equivalent dipole model to PVEP data.
• Correlating dipole orientation with surface amplitude topography.

Main Results:

• Visual inspection of PVEP surface amplitude distribution failed to reliably identify the stimulated hemifield in most subjects (15/28).
• The single equivalent dipole model correctly identified the stimulated hemisphere in 25 out of 28 hemifield PVEPs.
• Dipole orientation, particularly tangential orientations, correlated with ipsilaterally predominant P100 surface topography.
• Dipole locations were sometimes anterior or inferior to the occipital lobe, indicating potential limitations.

Conclusions:

• A single equivalent dipole model provides a more reliable method for identifying the stimulated hemisphere compared to surface topography analysis.
• Dipole modeling offers valuable insights into the source localization of surface-recorded visual evoked potentials.
• Understanding dipole orientation is crucial for interpreting variable PVEP surface topography.