Banca de QUALIFICAÇÃO: JULIO CESAR DA COSTA MOURA

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : JULIO CESAR DA COSTA MOURA
DATE: 20/09/2021
TIME: 09:00
LOCAL: meet.google.com/pvr-tjua-qex
TITLE:

Spike-field coherence in the low-gamma band of the primary visual cortex of agouti and cats

KEY WORDS:

cat, agouti, V1, low-gamma, oscillation, spike-field coherence

PAGES: 63
BIG AREA: Ciências Biológicas
AREA: Fisiologia
SUMMARY:

Neural oscillations in the low gamma band (30-49 Hz) have been related to visual processing. Spike-field coherence is an established measure to study neural synchronicity and communication between two neural groups but can also be applied to study the coordination of spiking activity and the local field potential as a signature of functional cortical layout and local connectivity. Along the same line, the phase-locking value (PLV) is used to study oscillatory activity between local field potential (LFP) and spiking activity. It was observed previously, that cats present spike-field phase locking in in the low gamma band of V1, which is tuned to the same orientation as the spike rate. Cats exhibit their orientation-selective neurons organized in periodic columns arranged in pinwheel-like structures. Therefore, the interpretation that the strong and tuned interactions between spikes and local field potentials of the same electrode could reflect the orderly columnar layout when stimulating with salient oriented visual stimuli, stands to reason. All visual rodents investigated so far – including the large visual rodent agouti - possess orientation-selective neurons and present robust responses to oriented gratings. However, they do not express regular maps as cats or primates, but, if at all, mini-columns interspersed with “salt-and-pepper” regions. Although agouti neurons occasionally exhibit oscillatory spiking and LFP activity in the low gamma range this activity is almost never tuned to the same orientation as the spike rate confirming the hypothesis that a columnar layout facilitates the occurrence of tuned oscillations. In the present thesis, we aimed to further elucidate the role of oriented whole-field gratings in driving the tuned coherent gamma oscillations in visual cortices with a columnar versus a non-columnar layout. Therefore, we compared spiking and LFP activity in cat and agouti primary visual cortex evoked by evoked by whole-field stimuli of different saliency, containing less or no orientation component, namely gratings, random-dot textures and textures of randomly placed oriented bars. In detail, we examined whether absolute mean firing rate, Fano-factor, spike-field coherences and frequencies, cross-spectrum of frequencies (cross-spectrum OS) and frequencies, PLV and OSI evoked by the three different stimulus types vary in a species-specific manner, which could be explained by the supposedly different functional layouts. To this end, we have analyzed the metrics for LFP-MUA and LFP-SUA activities in visual evoked potential and sustained phase windows in which OSI > 0.1, and absolute mean firing rate > 2.00 spikes/secs and absolute mean firing rate < 200.00 spikes/secs. Overall, firing rates, spike-field coherence and oscillation frequencies tend to be higher in cats than in agoutis for all stimulus types. We observed significant differences of raw spike-field coherence in the low gamma band between species for all three stimuli (p-Value of Mann–Whitney U test < 0.0001 for all stimuli in both LFP-MUA and LFP-SUA) during the sustained phase window (LFP-MUA – Agouti: bar: n=139; dot: n=104; grating: n=143; Cat: bar: n=351; dot: n=200; grating: n=399; LFP-SUA – Agouti: bar: n=221; dot: n=176; grating: n=226; Cat: bar: n=365; dot: n=230; grating: n=532). The same result is observed for spike-field coherence frequencies (p-Value of Mann–Whitney U test < 0.0001 for all stimuli in LFP-MUA and LFP-SUA).  Gratings seem to be more efficient than random-dot or bar textures in evoking high spike-field coherences in both species. This tendency is only significant in cats. Although agoutis follow that tendency, especially in the sustained response, the majority of metrics do not show a significant difference between the three stimuli and between species. Our result indicate that cats express more robust spike-field coherences than agoutis. Both layout types, columnar and interspersed networks, can express coherent low gamma oscillatory activity especially when challenged with optimally oriented gratings.

BANKING MEMBERS:
Interno - 3086031 - DANIEL YASUMASA TAKAHASHI
Presidente - 1871878 - KERSTIN ERIKA SCHMIDT
Interno - 1842426 - SERGIO TULIO NEUENSCHWANDER MACIEL