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Abstract:
Electrical microstimulation has been used extensively to study both neuronal connectivity and the behavioral effects of focal neural excitation. Yet most behaviors involve concurrent activation of several structures that are directly or indirectly interconnected with the stimulated site. Microstimulation performed simultaneously with fMRI offers a unique opportunity to investigate the network of structures eliciting certain behaviors. Recently, simultaneous recording of neural activity and BOLD responses in the monkey has been developed to study the correlation between the fMRI signals and electrical activity in the brain (Logothetis et al., 2001). This work has also enabled us to carry out simultaneous electrical microstimulation and fMRI. The specific goal of the current study is to determine the electrical parameters which elicit activity in the brain similar to that generated by focal visual stimulation. We compared visual stimulation with constant-current charge-balanced biphasic electrical pulses delivered via monopolar microelectrodes placed in area V1. We find that under certain microstimulation parameters we obtain focal activity around the electrode tip in area V1 as well the corresponding retinotopic location in area V2, V3, and MT. Ongoing research examines the activity patterns elicited by stimulating at different cortical layers of V1. This study paves the way to incorporate the much needed anatomical information in the analysis of the electrical signals obtained in trained, awake animals.
