The Department of Cognitive Sciences and Center for Cognitive Neuroscience present
"fMRI BOLD Response as a Function of Neuronal Activity"
with Bosco Tjan, Associate Professor, Department of Psychology, University of Southern California
Wednesday, March 13, 2013
Social & Behavioral Sciences Gateway (SBSG), Room 1517
Determining the relationship between neuronal activity and the BOLD response is hard not only because simultaneously measuring neuronal and BOLD activities is difficult but also because what constitutes as “neuronal activity” is not clear. Attempts to noninvasively infer this relationship from stimulus-BOLD response is severely hindered by the complex nonlinearity between stimulus and neuronal activity. Now consider a hypothetical system with two identical groups of non-interacting neurons that co-locate in the same capillary bed and control the same local vascular network. Further suppose that we can independently manipulate each group with stimuli. This system would be ideal for mapping the relationship between neuronal activity and BOLD response, circumventing the unknown relationship between stimulus and neuronal activity and the unknown composition of neuronal activity – presenting identical stimuli to both groups of neurons will, by definition, double the neuronal activity in the local region. Tjan has found just such an ideal system in the low-level visual areas of humans born without the optic chiasm. This was used in vivo system to quantify the relationship between neuronal and BOLD responses and to untangle hemodynamic nonlinearity from neuronal nonlinearity in phenomena such as fMRI adaptation, surround suppression, and spatial summation.
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