Neuronal Functional Connection Graphs among Multiple Areas of the Rat Somatosensory System during Spontaneous and Evoked Activities

Abstract

Small-World Networks (SWNs) represent a fundamental model for the comprehension of many complex man-made and biological networks. In the central nervous system, SWN models have been shown to fit well both anatomical and functional maps at the macroscopic level. However, the functional microscopic level, where the nodes of a network are represented by single neurons, is still poorly understood. At this level, although recent evidences suggest that functional connection graphs exhibit small-world organization, it is not known whether and how these maps, potentially distributed in multiple brain regions, change across different conditions, such as spontaneous and stimulus-evoked activities. We addressed these questions by analyzing the data from simultaneous multi-array extracellular recordings in three brain regions of rats, diversely involved in somatosensory information processing: the ventropostero-lateral thalamic nuclei, the primary somatosensory cortex and the centro-median thalamic nuclei. From both spike and Local Field Potential (LFP) recordings, we estimated the functional connection graphs by using the Normalized Compression Similarity for spikes and the Phase Synchrony for LFPs. Then, by using graph-theoretical statistics, we characterized the functional topology both during spontaneous activity and sensory stimulation. Our main results show that: (i) spikes and LFPs show SWN organization during spontaneous activity; (ii) after stimulation onset, while substantial functional graph reconfigurations occur both in spike and LFPs, small-worldness is nonetheless preserved; (iii) the stimulus triggers a significant increase of inter-area LFP connections without modifying the topology of intra-area functional connections. Finally, investigating computationally the functional substrate that supports the observed phenomena, we found that (iv) the fundamental concept of cell assemblies, transient groups of activating neurons, can be described by small-world networks. Our results suggest that activity of neurons from multiple areas of the rat somatosensory system contributes to the integration of local computations arisen in distributed functional cell assemblies according to the principles of SWNs.

Electrophysiological effects of non-invasive Radio Electric Asymmetric Conveyor (REAC) on thalamocortical neural activities and perturbed experimental conditions

“…More in detail, the electrophysiological signals were digitized and recorded with bandpass at 6 kHz/300 Hz for spikes, 180 Hz/1 Hz for Local Field Potentials (LFP). The data stored were analyzed off-line both using Matlab-based functions and by locally developed software 13 .…”

“…To return a better characterization of the involved brain circuits, we analyzed the recorded data both from the perspective of the single neurons and from the perspective of the network of the involved neurons 11 12 . To this purpose we used a method previously worked out in our lab, namely an analytical framework to combine these two multiscale featuring 13 .…”

A novel wireless recording and stimulating multichannel epicortical grid for supplementing or enhancing the sensory-motor functions in monkey (Macaca fascicularis)

“…To this purpose, we used the stimulation device together with a novel stimulus delivery protocol and a predictive computational framework. The protocol of randomizing stimuli offered the advantage of paired pulses and reduced the possibility of spurious locking between stimuli and spontaneous periodical bursts of neuronal activity and sensory habituation with waning responses to equal subsequent stimuli (Zippo et al, 2013 , 2014 ).…”

Sending all the right signals

“…Similar to the data management approach we took in Chapter 3, each set of links (i.e., edge set) is separated into network layers, which can be treated both as individual networks, and as a composite of individual networks, producing a multigraph (see: Figure 1 and Zippo, Storchi, Nencini et al, 2013). Meeting participants also complete a dyadic mutual evaluation (DME) exercise, where each participant rates their creative ties with every other participant with regard to creative outcomes during the meetings, as part of project debriefing, informed by research precedent for social-network-based peer evaluation (Luria & Kalish, 2013).…”

“…The complete dataset was made up of six types of NVSI (i.e., PRX, F2F, TTK, BMM, PM, and VM) for each of the teams with 19 and 16 team members respectively. Each NVSI is separated into layers (one for each 30-minute increment within a meeting), which can be treated both as individual networks, and together, producing a multigraph or a multiplex network (Zippo et al, 2013). The dataset for TG was comprised by the 19 team members, the six NVSI, and the 78 sessions adding up to 4211 dyads (or 468 matrices).…”