PUBLICATIONS

Functional architecture matters in the formation of perception.

Elimination of false matches is a multistep process. V2 is an important step in the process. We show that by integrating disparity domain neuron responses with similar preferred disparity but across different preferences of other visual features (including spatial scale, receptive field size, and phase disparity, based on previously published data), our model preserves responses to correct matching and greatly attenuates responses to false matching. We extend the energy model to a population levelto account for our findings in V2. We start with neurons similar to previously described single-neuron responses: Each neuron is responsive to both correct and to false  matches as predicted by the energy model. Based on an estimate of 110,000 neurons per cubic millimeter of cortical tissue and the average size of a V2 disparity cluster of 3.5 mm3  for 10–15 different disparities within that cluster, each would integrate on the order of 30,000 neurons. We further estimated the number of neurons needed in the population to achieve a result that predicts the percept. To do this, we defined the “perceptual index” for different numbers of neurons in the population model. A perceptual index value of 100 indicates complete discarding of false matches and is close to the subject’s depth percept, while a value of 0 indicates no attenuation to false matches. By examining a range of populations from 2 neurons to 100,000 neurons, the ability to discard false matching increases: the more neurons included, the lower the response to false matching. With as few as 250 neurons, the amplitude of response to false matches is reduced by 91%. A disparity domain with 30,000 neurons, according to our model, eliminates 97% of false matches. An additional layer of pooling inputs from multiple V2 neurons within one disparity domain could further reduce aRDS response among single neurons in V4 and inferior temporal cortex. These simulations illustrate that V2 can respond to correct matches and reject false ones by pooling over the population. The greater the numbers pooled, the better the performance. By pooling over a population of neurons with similar disparity preference, binocular correspondence for depth percept can be established.

Yin H, Fu P, Lu H, Tanigawa H, Roe A, Chen G*. Reply to Doi et al.: Functional architecture matters in the formation of perception. PNAS. 115(30):E6969-E6971. *Corresponding author. Impact Factor = 9.504


Microelectrode array stimulation combined with optical imaging: A novel tool for brain mapping

Chernov M, Chen G, Torre-Healy L, Friedman R, Roe A. Microelectrode array stimulation combined with intrinsic optical imaging: a novel tool for functional brain mapping. Journal of  Neuroscience Methods, 263:7-14. Impact Factor = 2.668

Infrared neural stimulation of primary visual cortex in non-human primates

Infrared neural stimulation (INS) is an alternative neurostimulation modality that uses pulsed infrared light to evoke spatially precise neural activity that does not require direct contact with neural tissue. With these advantages INS has the potential to increase our understanding of specific neural pathways and impact current diagnostic and therapeutic clinical applications. In order to develop this technique, we investigate the feasibility of INS (λ=1.875μm, fiber diameter=100-400μm) to activate and modulate neural activity in primary visual cortex (V1) of Macaque monkeys. Infrared neural stimulation was found to evoke localized neural responses as evidenced by both electrophysiology and intrinsic signal optical imaging (OIS). Single unit recordings acquired during INS indicated statistically significant increases in neuron firing rates that demonstrate INS evoked excitatory neural activity. Consistent with this, INS stimulation led to focal intensity-dependent reflectance changes recorded with OIS. We also asked whether INS is capable of stimulating functionally specific domains in visual cortex and of modulating visually evoked activity in visual cortex. We found that application of INS via 100μm or 200μm fiber optics produced enhancement of visually evoked OIS response confined to the eye column where INS was applied and relative suppression of the other eye column. Stimulating the cortex with a 400μm fiber, exceeding the ocular dominance width, led to relative suppression, consistent with involvement of inhibitory surrounds. This study is the first to demonstrate that INS can be used to either enhance or diminish visual cortical response and that this can be done in a functional domain specific manner. INS thus holds great potential for use as a safe, non-contact, focally specific brain stimulation technology in primate brains.

 Cayce J, Friedman R, Chen G, Jansen E, Mahadevan-Jansen A, Roe A. Infrared neural stimulation of primary visual cortex in non-human primates. Neuroimage. 84:181-90. Impact Factor = 5.426


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