Contributions of prefrontal and extrastriate cortex to the event-related potential index of attention

点击翻译按钮获取中文摘要

PROJECT SUMMARY Attention improves behavior by enhancing visual processing and suppressing distracting information. Research into neural mechanisms of visual attention relies heavily upon a key event-related potential in the electroencephalogram (EEG) known as the N2pc. The N2pc reliably indicates where and when attention is allocated. Discovered in humans, the N2pc has been observed in macaque monkeys. The neuronal origins of the N2pc are unknown. Several investigators have suggested that extrastriate visual area V4 is the main contributor to the N2pc. However, while V4 shows some of the most pronounced responses to attentional selection in occipital cortex, it is not the only area to do so. Moreover, concurrent EEG and single-unit recordings in the frontal eye field (FEF) revealed that prefrontal neurons indicate attentional selection before the N2pc manifests on the scalp. Given the extensive anatomical connections between FEF and V4, V4 could generate the N2pc consequent to feedback from FEF. This hypothesis has never been tested, so the research goal of this project is to elucidate the neural origins of the N2pc. I will test the hypothesis that V4 activity can contribute to the N2pc (Aim 1) and the hypothesis that FEF is the initiator of this attentional signal (Aim 2). Aim 1 will be addressed through laminar recordings of area V4 concurrent with extracranial EEG during visual search. I will use these data to determine whether V4 activity can contribute to the N2pc by estimating the relationship between net synaptic depolarizations (i.e., Current Source Density) and the EEG signal. Furthermore, I will forward model the EEG using the current dipoles measured across V4 layers to investigate their role in N2pc generation. Aim 2 will be addressed by reversibly inactivating V4 and FEF to test whether or not the N2pc survives these causal manipulations. The outcome of these studies will provide definitive answers about the neural generators of one of the most commonly used biophysical indicators of attention. The primary training objective of this proposal is to attain expertise in the required skill set, bridging between human EEG and animal neurophysiology. This will include gaining expertise in the relevant literature, learning multi-site, multi-channel laminar recording techniques, learning to perform EEG, and learning to perform reversible inactivation studies. All of this will be guaranteed via mentorship by my co-sponsors Drs. Alexander Maier and Geoffrey Woodman as well as my advisory collaborators Drs. Jeffrey Schall, John Reynolds, and Jorge Riera.