Brainmap: Shahin Nasr, PhD- Application of high resolution fMRI in studies of fine-scale cortical structures

Abstract

It is widely known that almost all cortical areas consist of heterogeneous fine-scale neural clusters that show different selectivity and response profile and play different functional roles.  However, due to the low spatial resolution of neuroimaging techniques, especially in human studies, this heterogeneity is usually ignored, and cortical areas are treated as one single homogenous unit.  Unfortunately, this may lead to wrong and misleading interpretations of neuroimaging results about the functional role of cortical areas. Secondary visual area (V2) is a good example of this heterogeneity.  More than 30 years ago, histological studies in non-human primates showed that V2 consists of three different stripe-shape structures.  These fine-scale structures were categorized into thin, thick and pale stripes according to their size and their level of myelination.  Subsequent single cell and optical imaging studies showed that these stripes serve different functional purposes, and are part of segregated processing streams. In humans, until recently, evidence for such fine-scale cortical structures was limited to a handful of postmortem histological studies. Due to the low spatial resolution of the conventional neuroimaging techniques, no previous study had shown any functional evidence for these stripes, and V2 was treated as one homogenous cortex. 

Recently, by taking advantage of high-resolution fMRI based on using ultra-high field (7T) scanner, we demonstrated the first functional evidence for these stripes in humans (Nasr, Polimeni and Tootell, 2016).  We have also shown evidence for similar fine-scale cortical structures in the subsequent visual area V3. In this talk, I will start with a brief presentation of our recently published results.  Then, I will demonstrate our new findings about the functional properties of these fine-scale cortical structures (e.g. selectivity for color, disparity, shape and spatial frequency) in V2, V3, V3A and V4 and explain how ignoring this heterogeneity can lead to misinterpretation of the findings.      

Suggested  Readings:

-       Nasr, S., Polimeni, J. R., & Tootell, R. B. (2016). Interdigitated color-and disparity-selective columns within human visual cortical areas V2 and V3.The Journal of Neuroscience, 36(6), 1841-1857.

-       Nasr, S., & Tootell, R. B. (in press). Visual Field Biases for Near and Far Stimuli in Disparity Selective Columns in Human Visual Cortex. NeuroImage.

About the Speaker

I was born and raised in Tehran, Iran.  I received my B. S. (1999) and M. S. (2002) in Biomedical engineering from Shahid Beheshti Medical University (SBMU) and Iran University of Science and Technology (IUST) respectively.  I received my Ph. D. in cognitive neuroscience from the Institute for Research in Fundamental Sciences in 2009 under the supervision of Dr. Hossein Esteky. Then I moved to the U.S. to join Dr. Roger Tootell’s lab as a post-doc.  Since 2014, I have been an instructor in radiology at Harvard Medical School and assistant in neuroscience at Massachusetts General Hospital.