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Interaction of relative and absolute depth signals in the primate brain

Final Report Summary - REAL-DEPTH (Interaction of relative and absolute depth signals in the primate brain)

Concise overview of the progress of the work in line with the structure of Annex I of the Grant Agreement and summary of progress towards objectives and details for each task.

The scientific proposal contained two main experiments. The first one is related to the implication of vergence on the cortical activity during vision. The second one is related to the localization of cortical areas that encode the ‘real’ position of objects (i.e. relatively to the body and not relatively to the retina). These two experiments are performed on both human and non-human (macaque) primates.

Experiments in human: Following the detailed work plan described at page 21 of the scientific document, numerous fMRI recordings for the first experiment in human were performed during the first year of the funding. These recordings included 6 subjects who performed three two-hours sessions (see the mid-term report), which represents 36 hours of recordings. During the second year of the funding, these data were completed by recordings on 4 additional subjects (i.e. 24 hours of recordings). The analysis showed that eye vergence has an influence on the visual responses as early as area V1. These results were presented at two international conferences (Cottereau et al., ECVP 2014 and SFN 2014) and a publication is just about to be submitted.

Data for the second experiment were collected in four subjects (2 two-hours sessions per subjects for a total of 16 hours of recordings). Up to now, the analyses suggest that some areas of the surrounding space (e.g. the straight-ahead direction) are associated with enhanced fMRI responses in the visual cortex. Additional recordings on new subjects are currently performed to complete this study and to prepare a second publication on human data, in line with the schedule described with the proposal.

Experiments in macaque: the researcher performing the experiments (Benoit Cottereau) has been deeply involved in the development of monkey fMRI in the host laboratory. He participated in the training of four macaques and was implied in more than 100 hours of recordings. He was also involved in the development of an fMRI coil specifically dedicated to monkey fMRI that has been designed in collaboration with RapidBiomed. This new coil should arrive in the host laboratory by the end of the year and permit brain recordings of higher quality. Up to now, the data needed for the first and second experiments have been fully collected in one monkey and are currently being analyzed. The results suggest that the effects that were found in human also exist in macaque. Data are now collected on three additional monkeys and the results should be published by June 2015.

Benoit Cottereau also participated in a collaboration between the host laboratory and the Royal Holloway University in London (Professor Andrew Smith) for a study directly related to the topic of the proposal. The aim was to test if a cortical area that was recently discovered in human (CSv for Cingulate Sulcus visual) also exists in macaque. This area is specifically responding to egomotion compatible 3D optic flow and could therefore be involved in real-depth perception. Recordings were performed in macaques using the same protocol that permitted to discover this area in human. Our results suggest that the macaque brain has an homologue of this area. These results were presented at a national conference in 2013 (see Cottereau et al., 2013) and a paper is in preparation.

References:

- Cottereau BR, Durand JB, Vayssière N & Trotter Y: The influence of eye vergence on retinotopic organization in human early visual cortex. Annual meeting of the European Conference on Visual Processing (ECVP), August 24-28, Belgrade, Serbia and N & Annual meeting of the Society for Neuroscience. November 15-19, Washington, USA.

- Cottereau BR, Fize D, Trotter Y, Smith AM & Durand JB: Representation of egomotion in non-human primate. Annual meeting of French Society for Neuroscience (SNF), May 21-24, Lyon, France.

Summary of the progress of the researcher training activities/transfer of knowledge activities/integration activities (as it applies for the MC action)

The scientific document had established two main objectives for the transfer of knowledge (cf p.11 of the scientific document):

1- To develop in the host institution an imaging platform that will routinely define functional areas in both the monkey and human brain.

2- To characterize at the population level how real depth is encoded in these different functional areas in the primate brain.

The imaging platform described in point 1 has been established by the researcher and the definition of visual areas using functional magnetic resonance imaging (fMRI) is now performed routinely in both human and monkey in the host institution. Benoit Cottereau recently published a paper regarding how these functionally defined visual areas can be used for data fusion in multimodal neuroimaging (Cottereau et al., 2014).

Regarding point 2, the experiments described in the proposal have been performed (see the previous section) on the basis of the detailed work plan described in the scientific document (cf p. 21). The researcher is therefore directly contributing to understanding how real depth is processed in the primate brain.

Regarding the training, Benoit Cottereau has followed the courses to be legally authorized to perform research on animals independently and also courses to perform surgeries on animals. In November 2013, he followed a training for advanced fMRI data analysis organized by the European Society for Magnetic Resonance in Medicine and Society (ESMRMS) in Tubingen (Germany).

Regarding integration activities, Benoit Cottereau was recruited by the CNRS this year. He now has a tenure research position in the host laboratory. He is a member of the ECO-3D team (led by the principal investigator of this proposal Yves Trotter) and his research project is in the direct continuity of the experiments performed during the project. This recruitment will permit to complete the studies and publications associated with the proposal in the best conditions and to pursue new studies related to this field of research. In addition, Benoit Cottereau is also leading a research axis on multimodal imaging in the host institution. It will permit to maintain and develop the imaging platform described as one of the main objective for the transfer of knowledge.

References:

- Cottereau BR, Ales JM & Norcia AM: How to use fMRI functional localizers to improve EEG/MEG source estimation. Journal of Neuroscience Methods. In press.

Clearly significant results

The results of the first experiment in human strongly suggest that eye position (the vergence angle in particular) has a direct influence on the population responses of the early visual cortex. If these results were to be definitively confirmed in non-human primates, they would have a major impact on the neuroscience community because the current models of visual processing would need major revisions.

The results of the second experiment suggest that specific parts of the visual fields are associated with enhanced fMRI responses in the visual cortex. If these results were to be confirmed, it would also have a major impact in our current understanding of visual processing in the primate brain.