Banca de QUALIFICAÇÃO: BEATRIZ CARVALHO FROTA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : BEATRIZ CARVALHO FROTA
DATE: 17/02/2023
TIME: 08:30
LOCAL: INSTITUTO DO CEREBRO
TITLE:

Characterization of coherent pairs and interhemispheric neuronal assemblies activity in the primary visual cortex

KEY WORDS:

callosal connections, primary visual cortex and perceptual integration

PAGES: 117
BIG AREA: Ciências Biológicas
AREA: Fisiologia
SUMMARY:

Long-range selective horizontal connections might be decisive for the maintenance of a spontaneously active network that conditions “a priori” neuronal responses by facilitating likely conjunctions of forms, or of movement trajectories. Accordingly, fundamental principles of Gestalt, such as the grouping of elements according to orientation and collinear alignment, could be engineered by selective horizontal circuits, and ongoing functional interactions should reflect this architecture. In the primary visual cortex, these connections extend through the corpus callosum with the same selectivity for orientation, direction of movement and collinearity. Their position in the central visual field render possible to compare intra- with interhemispheric actions, representing trajectories and directions of movement crossing the vertical meridian of the visual field or not. To address possible neuronal signatures of those interactions we studied the activity of neurons representing midline crossing stimuli in the two visual cortices by recording simultaneously from 2 x 16 spatially separated electrodes, which were placed into homotopic parts of the visual cortex, i.e. the transition zone between area 17 and 18, in cats (n = 4). In order to implant electrodes into cortical sites that are directly or indirectly linked by the corpus callosum, we performed intrinsic signal imaging to precisely define the areal border. Subsequently, we obtained extracellular electrophysiological recordings of single unit spiking activity during grating and natural visual stimulation designed to study integration. As an efficient measure of functional interaction we used ongoing and stimulus-evoked coherence in the low gamma band (30-59 Hz) between pairs of firing rates, focusing on pairs of neurons with overlapping receptive fields and also with detection of Neural Assemblies. We compared this measure to joint rate changes as well as to changes of the joined Fano Factor. We observed significant ongoing and evoked coherence at least for one stimulus condition in the majority of intrahemispheric (n=447) and interhemispheric pairs (60%, n=266) of single units with overlapping RFs, with higher probability for intra- than interhemispheric pairs (73% versus 60%). On average, ongoing and evoked coherence between intra- was about 20% higher than between interhemispheric pairs. This difference increased to almost 35% for cases where both ongoing and stimulus driven activity showed significant coherence. Both types of coherence showed orientation and direction selectivity, in both ongoing and stimulus-driven activity. Intrahemispherically, the pairwise coherence decayed with cortical distance between iso-oriented neurons to peak again at an interval of about 900µm in accordance with the clustering of horizontal connections. In conclusion, we detected and characterized interhemispheric Assemblies in v1 and confirmed that both ongoing and stimulus-driven coherence within long- range intrinsic and interhemispheric networks reflect the selectivity of horizontal axons to link neurons of similar response properties over longer distances. The results are compatible with the interpretation that those connections serve to anticipate likely grouping operations between neurons representing the vertical meridian, such as those caused by crossing movements or objects. 

COMMITTEE MEMBERS:
Interno - 1721223 - ADRIANO BRETANHA LOPES TORT
Interno - 3086031 - DANIEL YASUMASA TAKAHASHI
Presidente - 1871878 - KERSTIN ERIKA SCHMIDT
Interno - ***.922.111-** - SERGIO ANDRÉS CONDE OCAZIONEZ