|Date & Location||Speakers|
|Monday, February 24
11:00am - 12:00pm
|Bosco S. Tjan, Associate Professor of Psychology at University of Southern California
Quantifying the Relationship Between the fMRI BOLD Signal and Neuronal Activity with an Achiasmic Human Subject
Quantifying the relationship between neuronal activity and the fMRI BOLD signal is difficult because “neuronal activity” is not a unitary quantity, and precisely measuring neuronal activity requires invasive techniques. Attempts to infer this relationship from stimulus-evoked BOLD responses have been frustrated by the complex nonlinearity between stimulus and neuronal activity. Here we describe a unique in-vivo model for non-invasively determining the relationship between neuronal and BOLD activity. We demonstrated that in the low-level visual cortex of a human subject who was born without optic chiasm, there are two nearly identical populations of non-interacting but co-locating neurons, with non-overlapping receptive fields. By presenting identical stimuli to both of these receptive fields instead of just one, we can double the local neuronal activity, regardless of the definition of “neuronal activity”. Using this in-vivo model, we found that BOLD response amplitude is proportional to approximately the square root of the underlying neuronal activity. (Joint work with Pinglei Bao and Chris Purington)
|Friday, March 7
3:00 pm - 4:00 pm
|Gaurav Patel, Columbia University
Structural/Functional Relationships of Attention Networks
Disorders of selective attention are common in psychiatric disorders yet remain poorly understood. In the human brain, selective attention is controlled by the interactions of frontoparietal areas comprising two networks--the dorsal and ventral attention networks. Relatively little is still known about the anatomical connectivity between these areas and the relationship between the anatomy and functions of these networks. The macaque is often used as a model system for the study of these structural/functional relationships. However, the direct comparison of the attention systems of humans and monkeys with fMRI reveals a number of basic differences between the two species, including the lack of a ventral attention system. These differences point to evolutionary changes between the two species in the attention networks as well as other frontoparietal networks, the very cortical networks often implicated in psychiatric disorders in humans. While studying the macaque as a model system continues to be fruitful for understanding principles that govern structural/functional relationships, the study of these evolved cortical networks may instead be advanced by combining advanced neuroimaging techniques with single-subject surface analysis methods in humans. Correlating structural/functional relationships with behavior on an individual basis may lead to more accurate targeting of treatments such as TMS, as well as a more clear understanding of the neural mechanisms of human selective attention.
Friday, April 18
3:00pm - 4:00pm
|Rachel Denison, Postdoctoral Fellow at NYU
Functional Mapping of the Magnocellular and Parvocellular Subdivisions of Human LGN
The magnocellular (M) and parvocellular (P) subdivisions of primate LGN are known to process complementary types of visual stimulus information, but a method for noninvasively defining these subdivisions in humans has proven elusive. To functionally map the M and P subdivisions of human LGN, we used high-resolution fMRI at high field (7T and 3T) together with a combination of spatial, temporal, luminance, and chromatic stimulus manipulations. We found that stimulus factors that differentially drive magnocellular and parvocellular neurons in primate LGN also elicit differential BOLD fMRI responses in human LGN and that these responses exhibit a spatial organization consistent with the known anatomical organization of the M and P subdivisions. Mapping LGN subdivisions opens possibilities for investigating their functions in human visual perception, in patient populations with suspected abnormalities in one of these subdivisions, and in visual cortical processing streams arising from parallel thalamocortical pathways.