LIP: The Gate of Frontal Feedback to Occipital Cortex?

Massachusetts General Hospital, Boston MA

Investigators

Abstract

Natural visual scenes usually contain a large number of items and objects. Unfortunately, the processing capacity of our brain is inadequate to simultaneously parse all details of incoming information. This problem can be partially solved, however, by selecting the most relevant stimuli in a scene which will be processed in more detail compared to 'irrelevant' items. There is ample evidence that this process, called 'visuospatial attention', increases perceptual and neuronal sensitivity at the attended location. It has been suggested that 'top-down' signals originating in a fronto-parietal network of areas can modulate neuronal activity in occipital visual cortex via feedback connections. However, very few studies have actually shown a causal relationship between activity in this fronto-parietal network and modulations of activity in visual cortex. With support from the National Science Foundation, Dr. Wim Vanduffel and his group seek to investigate at a whole-brain scale the causal nature of functional interactions between frontal and occipital areas. Therefore, he will combine functional Magnetic Resonance Imaging (fMRI) techniques with electrical intracranial microstimulation (EM) in an animal model. Dr. Vanduffel will test whether the artificially increased output of a specific frontal area can lead to spatially specific alterations of sensory-driven activity in occipital cortex. If so, Dr. Vanduffel will investigate i) the extent of the functional network involved, ii) the stimulus specificity of the modulations, and iii) whether artificially induced modulations of sensory-driven activity mimic spatial attention effects. Finally, by combining fMRI with reversible deactivation techniques he will study whether specific parietal nodes within this functional network are crucially involved in the transfer of top-down information from frontal to occipital cortex. The combination of the proposed experiments will move functional neuro-imaging from a mere mapping exercise to a real exploration of functional network dynamics, revealing mechanisms of cortical processing. Several undergraduate and graduate students will be trained during the activities sponsored by the National Science Foundation. Also, the proposed research will have a broader significance for fundamental research as the novel EM-fMRI method will provide a tool for detailed investigation of the functional role of feedback connections. These connections are poorly understood though increasingly viewed as crucial for understanding functional brain properties. The experiments may also have considerable clinical relevance for neurosurgeons performing peri-operative electrical stimulations. Moreover, the results of this project will also extend our theoretical understanding of attention deficits and may lead to the development of new analytical and diagnostic tools for attentional disorders.