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Columnar connectome: towards a mathematics of brain function. Network Neuroscience

Understanding brain networks is important for many fields, including neuroscience,
psychology, medicine, and artificial intelligence. To address this fundamental need, there are multiple ongoing connectome projects in the United States, Europe, and Asia producing brain connection maps with resolutions at macro- and microscales. However, still lacking is a mesoscale connectome. This viewpoint explains the need for a mesoscale connectome in the primate brain (the columnar connectome), presents a new method for acquiring such data rapidly on a largescale, and proposes how one might use such data to achieve a mathematics of brain function.

Roe, A. W. (2019). Columnar connectome: toward a mathematics of brain function. Network Neuroscience.Advance publication.

https://doi.org/10.1162/netn_a_00088

Columnar connectome towards a mathematics of brain function..pdf

Focal infrared neural stimulation with high-field functional MRI: A rapid way to map mesoscale brain connectomes

We have developed a way to map brain-wide networks using focal pulsed infrared neural stimulation in ultrahigh-field magnetic resonance imaging (MRI). The patterns of connections revealed are similar to those of connections previously mapped with anatomical tract tracing methods. These include connections between cortex and subcortical locations and long-range cortico-cortical connections. Studies of local cortical connections reveal columnar-sized laminar activation, consistent with feed-forward and feedback projection signatures. This method is broadly applicable and can be applied to multiple areas of the brain in different species and across different MRI platforms. Systematic point-by-point application of this method may lead to fundamental advances in our understanding of brain connectomes.

Xu GA, Qian M, Tian F, Xu B, Friedman RM, Wang J, Sone X, Sun Y, Chernov MM, Cayce JM, Jansen ED, Mahadeven-Jansen A, Zhang X, Chen G, Roe AW (2019) Focal infrared neural stimulation with high-field functional MRI: A rapid way to map mesoscale brain connectomes. SCIENCE ADVANCES. DOI: 10.1126/sciadv.aau7046

https://advances.sciencemag.org/content/5/4/eaau7046

Guohua - 2019 - Focal infrared neural stimulation with high-field .pdf

Subdomains within orientation columns of primary visual cortex

In the mammalian visual system, early stages of visual form processing begin with orientation selective neurons in primary visual cortex (V1). In many species (including humans, monkeys, tree shrews, cats, and ferrets), these neurons are organized in beautifully arrayed pinwheel-like orientation columns, which shift in orientation preference across V1. However, to date, the relationship of orientation architecture to the encoding of multiple elemental aspects of visual contours is still unknown. Here, using a novel highly accurate method of targeting electrode position, we report for the first time the presence of three subdomains within single orientation domains. We suggest that these zones subserve computation of distinct aspects of visual contours, and propose a novel tripartite pinwheel-centered view of an orientation hypercolumn.

Subdomains within orientation columns of primary visual cortex.pdf

Solving visual correspondence between the two eyes via domain-based population encoding in nonhuman primates

Stereoscopic vision depends on correct matching of corresponding features between the two eyes. It is unclear where the brain solves this binocular correspondence problem. Although our visual system is able to make correct global matches, there are many possible false matches between any two images. Here, we use optical imaging data of binocular disparity response in the visual cortex of awake and anesthetized monkeys to demonstrate that the second visual cortical area (V2) is the first cortical stage that correctly discards false matches and robustly encodes correct matches. Our findings indicate that a key transformation for achieving depth perception lies in early stages of extrastriate visual cortex and is achieved by population coding.

Chen G, Lu HD, Tanigawa H, and Roe AW (2017) Proc Natl Acad Sci 114(49):13024-13029.

http://www.pnas.org/content/114/49/13024.abstract

Solving visual correspondence between the two eyes via domain-based population encoding in nonhuman primates.pdf

Intrinsic signal optical imaging of visual brain activity: Tracking of fast cortical dynamics

Hemodynamic-based brain imaging techniques are typically incapable of monitoring brain activity with both high spatial and high temporal resolutions. In this study, we have used intrinsic signal optical imaging (ISOI), a relatively high spatial resolution imaging technique, to examine the temporal resolution of the hemodynamic signal. We imaged V1 responses in anesthetized monkey to a moving light spot. Movies of cortical responses clearly revealed a focus of hemodynamic response traveling across the cortical surface. Importantly, at different locations along the cortical trajectory, response timecourses maintained a similar tri-phasic shape and shifted sequentially across cortex with a predictable delay. We calculated the time between distinguishable timecourses and found that the temporal resolution of the signal at which two events can be reliably distinguished is about 80 milliseconds. These results suggest that hemodynamic-based imaging is suitable for detecting ongoing cortical events at high spatial resolution and with temporal resolution relevant for behavioral studies.

Lu HD, Chen G, Cai J, Roe AW (2017) Neuroimage, 148:160-168.

http://doi.org/10.1016/j.neuroimage.2017.01.006

Intrinsic signal optical imaging of visual brain activity Tracking of fast cortical dynamics.pdf

Spatial Distribution of Attentional Modulation at Columnar Resolution in Macaque Area V4

Attention to a location in a visual scene affects neuronal responses in visual cortical areas in a retinotopically specific manner. Optical imaging studies have revealed that cortical responses consist of two components of different sizes: the stimulus-nonspecific global signal and the stimulus-specific mapping signal (domain activity). It remains unclear whether either or both of these components are modulated by spatial attention. In this study, to determine the spatial distribution of attentional modulation at columnar resolution, we performed cerebral blood volume (CBV)-based optical imaging in area V4 of monkeys performing a color change detection task in which spatial attention was manipulated. We found that spatial attention enhanced global signals of the hemodynamic responses, but did not affect stimulus-selective domain activities. These results indicate the involvement of global signals in neural processing of spatial attention. We propose that global signals reflect the neural substrate of the normalization pool in normalization models of attention.

Tanigawa H, Chen G, Roe AW (2016) Frontiers in Neural Circuits, 10:1-13.

http://10.3389/fncir.2016.00102

Spatial Distribution of Attentional Modulation at Columnar Resolution in Macaque Area V4..pdf

In vivo mapping of cortical columnar networks in the monkey with focal electrical and optical stimulation and imaging

There are currently largescale efforts to understand the brain as a connection machine. However, there has been little emphasis on understanding connection patterns between functionally specific cortical columns. Here, we review development and application of focal electrical and optical stimulation methods combined with optical imaging and fMRI mapping in the non-human primate. These new approaches, when applied systematically on a large scale, will elucidate functionally specific intra-areal and inter-areal network connection patterns. Such functionally specific network data can provide accurate views of brain network topology.

Roe AW, Chernov M, Friedman RM, Chen G (2015) Frontiers in Neuroanatomy, 9:135.

http://10.3389/fnana.2015.00135

In vivo mapping of cortical columnar networks in the monkey with focal electrical and optical stimulation and imaging..pdf

Specificity of V1-V2 orientation networks in the primate visual

The computation of texture and shape involves integration of features of various orientations. Orientation networks within V1 tend to involve cells which share similar orientation selectivity. However, emergent properties in V2 require the integration of multiple orientations. We now show that, unlike interactions within V1, V1–V2 orientation interactions are much less synchronized and are not necessarily orientation dependent. We find V1–V2 orientation networks are of two types: a more tightly synchronized, orientation-preserving network and a less synchronized orientation-diverse network. We suggest that such diversity of V1–V2 interactions underlies the spatial and functional integration required for computation of higher order contour and shape in V2.

Roe AW and Ts'o DY (2015) Cortex,72:168-78.

http://doi.org/10.1016/j.cortex.2015.07.007

Specificity of V1-V2 orientation networks in the primate visual.pdf

Optogenetic Activation of Normalization in Alert Macaque Visual Cortex

Normalization has been proposed as a canonical computation that accounts for a variety of nonlinear neuronal response properties associated with sensory processing and higher cognitive functions. A key premise of normalization is that the excitability of a neuron is inversely proportional to the overall activity level of the network. We tested this by optogenetically activating excitatory neurons in alert macaque primary visual cortex and measuring changes in neuronal activity as a function of stimulation intensity, with or without variable-contrast visual stimulation. Optogenetic depolarization of excitatory neurons either facilitated or suppressed baseline activity, consistent with indirect recruitment of inhibitory networks. As predicted by the normalization model, neurons exhibited sub-additive responses to optogenetic and visual stimulation, which depended lawfully on stimulation intensity and luminance contrast. We conclude that the normalization computation persists even under the artificial conditions of optogenetic stimulation, underscoring the canonical nature of this form of neural computation.

Nassi JJ, Avery MC, Cetin AH, Roe AW, Reynolds JH (2015) Neuron, 86(6):1504-1517.

http://doi.org/10.1016/j.neuron.2015.05.040

Optogenetic Activation of Normalization in Alert Macaque Visual Cortex.pdf

Infrared neural stimulation: a new stimulation tool for CNS applications

The traditional approach to modulating brain function (in both clinical and basic science applications) is to tap into the neural circuitry using electrical currents applied via implanted electrodes. However, it suffers from a number of problems, including the risk of tissue trauma, poor spatial specificity, and the inability to selectively stimulate neuronal subtypes. About a decade ago, optical alternatives to electrical stimulation started to emerge in order to address the shortcomings of electrical stimulation. We describe the use of one optical stimulation technique, infrared neural stimulation (INS), during which short (of the order of a millisecond) pulses of infrared light are delivered to the neural tissue. Very focal stimulation is achieved via a thermal mechanism and stimulation location can be quickly adjusted by redirecting the light. After describing some of the work done in the peripheral nervous system, we focus on the use of INS in the central nervous system to investigate functional connectivity in the visual and somatosensory areas, target specific functional domains, and influence behavior of an awake nonhuman primate. We conclude with a positive outlook for INS as a tool for safe and precise targeted brain stimulation.

Chernov M and Roe AW (2014) Neurophotonics, 1(1):011011.

http://doi:10.1117/1.NPh.1.1.011011

Infrared neural stimulation a new stimulation tool for CNS applications.pdf

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