P316 Characterization of thalamic stimulus on a cortical column
Pablo Vizcaíno-García*1,2,3, Fernando Maestú1,3, Alireza Valizadeh1 Gianluca Susi1,2,3
1Zapata-Briceño Institute for Human Intelligence, Madrid, Spain. 2Department of Structure of Matter, Thermal Physics and Electronics, School of Physics, Complutense University of Madrid, Madrid, Spain 3Center for Cognitive and Computational Neuroscience, Complutense University of Madrid, Madrid, Spain
*Email: pabvizca@ucm.es
Introduction
Cortical columns are fundamental organizational units in cerebral cortical processing and development [1]. They regularly receive external stimuli, coming from both higher-order areas and the thalamus. Different hypotheses have been proposed regarding the function of the thalamus: it is considered to act as a generator of the alpha rhythm [2]; and it is also said to play a potential role in sensory gating. In this work we focus on exploring the latter process. We investigate how stimuli propagate from one layer of the cortical column to the entire unit, examining how alpha and gamma rhythms may be disrupted or enhanced across the different layers. We build upon the design of a cortical column by Potjans & Diesmann [3].
Methods We implemented an interconnected set of full-spiking cortical columns, each column encompassing 80000 neurons and 0.3 billion synapses. The connections have been derived from experimental data, utilising diffusion magnetic resonance imaging data. The column’s background stimulus was modified in order to start in a high-coherence state, which more easily allows the characterisation of the response. Said characterisation has been done by injecting a pulse packet into L4E, and obtaining order PRC (Phase Response Curves) which characterise the delays produced by the same stimulus if injected into different phases of the activity [4]. A 1ms wide stimulus was injected into different phases of the gamma period of L4E. Results The phases were identified after a gamma band filter (45-80Hz) and applying the Hilbert transform to the cortical column in the absence of a stimulus. The resulting PRC curves can be observed in Fig. 1. This figure presents both the raster plot of a stimulated cortical column and the resulting PRC curve. Each dot of the figure represents one spike of one neuron, in the appropriate time, and the superimposed line is the gamma-filtered population activity. From this figure we can observe there is a sudden halt in the gamma band after stimulation in L4E. The PRC curve was computed as an ensemble average of 10 trials. From this figure we highlight L23E as the only population which is consistently delayed by the input stimulus. Discussion From these early results, two main facts have become evident. First, the burst suppression phenomena emerges as a response to stimulating L4E, a layer that mostly receives its inputs from the thalamic nuclei. Second, the PRC of L23E shows the biggest time lag. Another avenue to explore is the variation of these curves in a less coherent network state. This work will seek to elucidate the mechanisms behind both of these phenomena, applying and comparing the results with the well-studied thalamocortical feedback loop. The investigation will contribute to a better understanding of the cortical column dynamics, but additionally will help clarify the effects of the communication between the thalamus and the cortical cortex.
Figure 1. Left: Raster plot of cortical column activity . Each dot represents a spike, and each colour a neuronal population. Imposed over the plot is the activity of each population, computed using a gaussian window over spike times, and normalised for the plot. Right: Phase response curve. Measures the time where each population reaches the first maximum in activity after stimulation injection into L4E. Acknowledgements This work was supported by Zapata-Briceño Intstitute of Science. References 1.https://doi.org/10.1016/B978-0-12-814411-4.00005-6 2. hhtps://doi.org/10.34734/FZJ-2023-02822 3.https://doi.org/10.1093/cercor/bhs358 4.https://doi.org/10.3389/fninf.2010.00006
