The influence of interhemispheric connections on ongoing and evoked orientation preference maps and spiking activity in the cat primary visual cortex

In the primary visual cortex, neurons with similar physiological features are clustered together in columns extending through all six cortical layers. These columns form modular orientation preference maps. Long-range lateral fibers are associated to the structure of orientation maps since they do not connect columns randomly; they rather cluster in regular intervals and interconnect predominantly columns of neurons responding to similar stimulus features. Single orientation preference maps – the joint activation of domains preferring the same orientation - were observed to emerge spontaneously and it was speculated whether this structured ongoing activation could be caused by the underlying patchy lateral connectivity. Since long-range lateral connections share many features, i.e. clustering, orientation selectivity, with visual inter-hemispheric connections (VIC) through the corpus callosum we used the latter as a model for long-range lateral connectivity. In order to address the question of how the lateral connectivity contributes to spontaneously generated maps of one hemisphere we investigated how these maps react to the deactivation of VICs originating from the contralateral hemisphere. To this end, we performed experiments in eight adult cats. We recorded voltage-sensitive dye (VSD) imaging and electrophysiological spiking activity in one brain hemisphere while reversible deactivating the other hemisphere with a cooling technique. In order to compare ongoing activity with evoked activity patterns we first presented oriented gratings as visual stimuli. Gratings had 8 different orientations distributed equally between 0º and 180º. VSD imaged frames obtained during ongoing activity conditions were then compared to the averaged evoked single orientation maps in three different states: baseline, cooling and recovery. Kohonen self-organizing maps were also used as a means of analysis without prior assumption (like the averaged single condition maps) on ongoing activity. We also evaluated if cooling had a differential effect on evoked and ongoing spiking activity of single units. We found that deactivating VICs caused no spatial disruption on the structure of either evoked or ongoing activity maps. The frequency with which a cardinally preferring (0º or 90º) map would emerge, however, decreased significantly for ongoing but not for evoked activity. The same result was found by training self-organizing maps with recorded data as input. Spiking activity of cardinally preferring units also decreased significantly for ongoing when compared to evoked activity. Based on our results we came to the following conclusions: 1) VICs are not a determinant factor of ongoing map structure. Maps continued to be spontaneously generated with the same quality, probably by a combination of ongoing activity from local recurrent connections, thalamocortical loop and feedback connections. 2) VICs account for a cardinal bias in the temporal sequence of ongoing activity patterns, i.e. deactivating VIC decreases the probability of cardinal maps to emerge spontaneously. 3) Inter- and intrahemispheric long-range connections might serve as a grid preparing primary visual cortex for likely junctions in a larger visual environment encompassing the two hemifields.

The influence of interhemispheric connections on ongoing and evoked orientation preference maps and spiking activity in the cat primary visual cortex

In the primary visual cortex, neurons with similar physiological features are clustered together in columns extending through all six cortical layers. These columns form modular orientation preference maps. Long-range lateral fibers are associated to the structure of orientation maps since they do not connect columns randomly; they rather cluster in regular intervals and interconnect predominantly columns of neurons responding to similar stimulus features. Single orientation preference maps – the joint activation of domains preferring the same orientation - were observed to emerge spontaneously and it was speculated whether this structured ongoing activation could be caused by the underlying patchy lateral connectivity. Since long-range lateral connections share many features, i.e. clustering, orientation selectivity, with visual inter-hemispheric connections (VIC) through the corpus callosum we used the latter as a model for long-range lateral connectivity. In order to address the question of how the lateral connectivity contributes to spontaneously generated maps of one hemisphere we investigated how these maps react to the deactivation of VICs originating from the contralateral hemisphere. To this end, we performed experiments in eight adult cats. We recorded voltage-sensitive dye (VSD) imaging and electrophysiological spiking activity in one brain hemisphere while reversible deactivating the other hemisphere with a cooling technique. In order to compare ongoing activity with evoked activity patterns we first presented oriented gratings as visual stimuli. Gratings had 8 different orientations distributed equally between 0º and 180º. VSD imaged frames obtained during ongoing activity conditions were then compared to the averaged evoked single orientation maps in three different states: baseline, cooling and recovery. Kohonen self-organizing maps were also used as a means of analysis without prior assumption (like the averaged single condition maps) on ongoing activity. We also evaluated if cooling had a differential effect on evoked and ongoing spiking activity of single units. We found that deactivating VICs caused no spatial disruption on the structure of either evoked or ongoing activity maps. The frequency with which a cardinally preferring (0º or 90º) map would emerge, however, decreased significantly for ongoing but not for evoked activity. The same result was found by training self-organizing maps with recorded data as input. Spiking activity of cardinally preferring units also decreased significantly for ongoing when compared to evoked activity. Based on our results we came to the following conclusions: 1) VICs are not a determinant factor of ongoing map structure. Maps continued to be spontaneously generated with the same quality, probably by a combination of ongoing activity from local recurrent connections, thalamocortical loop and feedback connections. 2) VICs account for a cardinal bias in the temporal sequence of ongoing activity patterns, i.e. deactivating VIC decreases the probability of cardinal maps to emerge spontaneously. 3) Inter- and intrahemispheric long-range connections might serve as a grid preparing primary visual cortex for likely junctions in a larger visual environment encompassing the two hemifields.

Cartas oficiais norte-riograndenses dos séculos XVIII, XIX e XX : constituição e caracterização de um corpus diacrônico

The diachronic studies marked the first decades of the 20th century in Brazilian linguistics, passing by an ostracism period after the 50s. Mainly from the 90s especially with the project, created in 1997, Para a história do português brasileiro (PHPB), which has systemized, in national ambit, the programme related to the area of diachrony the historical studies retake forces and have gradually increased since then. Our work is set in the new scene of Brazilian historical linguistics and it is associated to two research programmes: i) the constitution of a diachronic corpus; ii) the diachrony of text and discourse. As regards the first programme, we made effort to constitute a diachronic corpus of official letters about Rio Grande do Norte, we called cartas oficiais norte-rio-grandenses, written in 18th, 19th and 20th centuries. The chosen for bureaucrat letters occurred for they represent a textual category very productive in historical contexts, mostly 18th and 19th centuries, in which the command of writing was the least and also because they bring, almost always explicitly, the information of where, when, for whom and from whom, as remembers Fonseca (2003). The rules for constituting the corpus were based, although not strictly, on the orientation from PHPB. In respect to the second programme, we set up on the ideas of coserian base came from the studies on discourse traditions (TD) (Koch, 1997; Kabatek, 2006) amongst which that the texts are shaped so as to follow their own tradition (Coseriu, 2007), and we turned to Diplomatics (Belloto, 2002) in order to do the characterization of this corpus by the application of concepts from Diplomatics and TD as well as by the presentation of the structures that form those official letters: their textual genres, a kind of TD, with their macrostructures; and some of their formulaic expressions (microstructures), another sort of TD. This stage of characterizing will pay attention, as far as possible, to the dynamic between tradition and innovation that happen in the actualization of those textual structures along the centuries. This work intends to contribute with the researches connected to Historical Linguistics in Rio Grande do Norte, more specifically the ones related to the constitution of diachronic corpora and to TD; and with the study of official documents, textual category about which there are almost no studies (cf. Silveira, 2007)

Tatuagem da palavra : educação sentimental do corpo no corpus poético de Maria Teresa Horta

While looking to the body and finding it engraved by cultural, imaginary and power-related texts through a discourse embodied in itself, this research proposes a new vertiginous approach to it by analyzing the following works: Poesia completa II, more specifically, Educação sentimental, and Novas cartas portuguesas. Such transgressive and performatic works are from Maria Teresa Horta (1937-), Portuguese writer, who proposes a new education by a renewed language: a sentimental education spawned from the erotic element. Starting from the deconstruction of the view over the spoiled body and exposed in Novas cartas portuguesas, from the poetic texts in Educação sentimental, as well as in remaining ones in Poesia completa II, Horta disassembles and reassembles the body, giving a new meaning to the symbols that surround us and our experiences. Other than proposing to all, men and women, such new meaning of the behavior and current practices models, Horta s education allows, through a performance action, the construction of a stage for female identity, free from the phallic influence. A new identity, able to handle all holy and profane characteristics of women, discarding the chromatic lens of sin. Horta s poetry emerges as a new proposal of literary labor