Interactive Dipole Fitting and Simultaneous Retinotopy (IDSR)


IDSR Matlab Interface

The Interactive Dipolefitting
and Simultaneous Retinotopy (IDSR) technique uses a four-minute Pattern Pulse multifocal Visual Evoked Potential (PPmfVEP) and a structural MRI to create dipole source models.

With the created dipole source model, EEG recordings from visual stimuli are decomposed into their V1 and V2 currents.

VEP scalp plot with V1 and V2 waveform

mfVEP scalp plot from dartboard region 56.                            Decomposed V1 and V2 currents.

Distinguishing between close spaced sources is a difficult problem in dipole source analysis, especially between areas V1 and V2. Using an fMRI retinotopic map has shown good success as an additional constraint to solve the close source problem.

IDSR replaces the fMRI step with a user driven and computer driven optimization using mfVEP and a structural MRI. This greatly simplifies the dipole fitting process because an experimenter performing dipole analysis will already have the equipment and expertise to record a mfVEP with EEG or MEG. Additionally, IDSR removes the time, cost, and reliability issues in fMRI retinotopy, while retaining the benefits of a retinotopic map in distinguishing between close sources and cancellation due to cortical folding.

Inverso, S. A. “Evoked Currents in Human Visual Cortex.” (PhD Dissertation) The Australian National University, Canberra, ACT, AU (2010).

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