Scientists in Japan Identify Two Brain Circuits Involved in Image Recognition; Neurolucida Plays Part

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A monkey spots a mango and part of its brain lights up. The action takes place in the inferior temporal cortex, part of the brain that’s essential to object recognition. Using retrograde tracing and anatomical imaging, scientists at the National Institute of Neuroscience, and the RIKEN Brain Science Institute in Japan identified two interwoven, yet distinct, systems within the region’s complex circuitry.


“Our anatomical findings provide evidence for a recurrent network of at least two parallel systems,” the authors say in their paper published last December in Scientific Reports.


One system may send information about an object’s visual characteristics rapidly from one part of the inferotemporal cortex to the other, while the second system might work on a more local level, possibly helping to “compute multipart shape configurations,” the authors hypothesize.


To visualize the patching and circuitry of the cortical cells, the researchers developed a two-step method with retrograde tracing and fluorescent in vivo surface connection imaging. They first injected red fluorescent tracer into the anterior inferotemporal cortex (TE) of rhesus macaques. This revealed patches of feedforward neurons that projected from the posterior inferotemporal cortex (TEO), and provided a guide for a second tracer injection in green. Once stained, the circuits offered a clearer visual so that the researchers could examine the spatial relationship between the two systems more efficiently.


What they saw was a pair of “parallel, spatially intermingled circuits,” with one circuit projecting from the TEO to the TE, and a second circuit projecting “widely in the intrinsic network,” but not venturing to the other side of the inferior temporal cortex. “These parallel systems might be specialized for, respectively, fast vs. highly processed signals,” they explain.


The researchers quantified and plotted neurons with Neurolucida, and calculated distances between patches with Neurolucida Explorer, according to the paper.


Ichinohe, N., Borra, E., Rockland, K., (2012). Distinct Feedforward and Intrinsic Neurons in Posterior Inferotemporal Cortex Revealed by in Vivo Connection Imaging, Sci. Rep., 2(934). doi:10.1038/srep00934