Banca de DEFESA: SERGIO ANDRÉS CONDE OCAZIONEZ

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE: SERGIO ANDRÉS CONDE OCAZIONEZ
DATA: 31/03/2014
HORA: 09:00
LOCAL: Instituto do Cérebro
TÍTULO:

The influence of visual inter-hemispheric connections on spiking, assembly and LFP activities, and their phase relationship during figure-ground stimulation.

PALAVRAS-CHAVES:

Visual Cortex, Local Field Potential, Assemblies, Context stimuli.

PÁGINAS: 96
GRANDE ÁREA: Ciências Biológicas
ÁREA: Fisiologia
RESUMO:

Since Hubel and Wiesel’s pioneer finding a vast body of literature has accumulated describing neuronal responses in the primary visual cortex (V1) to different visual stimuli. These stimuli mainly consisted of moving bars, dots or gratings which served to explore the responses to basic visual features such as orientation, direction of motion or contrast, among others, within a classical receptive field (CRF). However, in the last two decades it became increasingly evident that the activity of V1 neurons can be modulated by stimulation outside their CRF. Thus, early visual areas might be already involved in more complex visual tasks like, for example, the segmentation of an object or a figure from its (back)-ground. It is assumed that intrinsic long-range horizontal connections within V1 as well as feedback connections from higher visual areas are actively involved in the figure-ground segmentation process. Their possible role has been inferred from the analysis of the spike rate variations induced by stimuli placed outside the CRF of single neurons. Although it is very likely that those connections also have an impact on the joined activity of neurons involved in processing the figure and on their local field potentials (LFP), these issues remain understudied.

In order to examine the context-dependent modulation of those activities, we recorded spikes and LFPs in parallel from up to 48 electrodes in the primary visual cortex of anesthetized cats. We stimulated with composite grating and natural scene stimuli focusing on populations of neurons whose CRFs were situated on the foreground figure. In addition, in order to examine the influence of horizontal connections we removed the inter-hemispheric input of the isotopic contralateral visual areas by means of reversible cooling deactivation.

We did so because i) the intrinsic horizontal connections cannot be easily manipulated without directly affecting the measured signals, ii) because inter-hemispheric connections share the major anatomical features with the intrinsic lateral network and can be seen as a functional continuation of the latter across the two hemispheres and iii) because cooling causally and reversibly deactivates input connections by temporarily silencing the sending neurons and thus enables direct conclusions on their contribution.

Our results demonstrate that the figure-ground segmentation mechanism is reflected in the spike rate of single neurons, as well as in their LFP power and its phase-relationship to the spike patterns produced by the population. In addition "lateral" inter-hemispheric connections modulate spike rates and LFP power depending on the stimulation of the neurons’ CRF surround. Further, we observe an influence of this lateral circuit on field-
field coherences between remote recording sites. In conclusion, our findings support the idea of complex figure-ground segmentation mechanism acting already in early visual areas on different time scales. This mechanism seems to involve groups of neurons firing synchronously and dependent on the LFP’s phase. Our results are also compatible with the hypothesis that long-range lateral connections contribute to that mechanism.

MEMBROS DA BANCA:
Interno - 1721223 - ADRIANO BRETANHA LOPES TORT
Externo à Instituição - JEAN CHRISTOPHE HOUZEL - UFRJ
Externo à Instituição - JEROME PAUL ARMAND LAURENT BARON - UFMG
Presidente - 1871878 - KERSTIN ERIKA SCHMIDT
Interno - 1842426 - SERGIO TULIO NEUENSCHWANDER MACIEL