Optogenetic investigation of cortical layer-6 neuron contributions to dynamic visual perception

In order to achieve a more complete understanding of neocortical brain function in health and disease, we need to delineate the computations of specific cell populations and how they dynamically exert their impact on connected target neurons. Here we’ve targeted neurons in the lateral geniculate nucleus (LGN) and in primary visual cortex (V1) using modern optogenetic methods that allow selective activation of neurons in the presence of light. Combining optogenetic stimulation with functional magnetic resonance imaging enables us to delineate the large scale cortical and subcortical connectivity of optogenetic activation. By assessing the electrophysiological activation we are able to characterize how this is locally reflected at the level of single neurons or synaptic activation patterns in the different layers of cortex. These assessments of neural function at the meso- and macro-scale are accompanied by behavioural assessment to what extent optogenetically evoked activation patterns can evoke visual phosphenes or bias visually based behaviour. By delineating the neural mechanisms by which optogenetic activation creates or modifies visual behaviour, our work is a first step towards building an optogenetics based prosthetic device that aims to improve vision under conditions of blindness. Establishing these methods first in non-human primates (NHP) is an important step towards translation of these methods to the human brain.

In a first set of experiments, we performed optogenetic injections into LGN of NHP. This enabled the selective targeting of so-called konio neurons and the investigation of their visual function. We found that less than 50% of these neurons were visually responsive at least under anaesthesia and that their projection to V1 influenced visual responses in V1’s supragranular layers. The results of this work are published in Klein et al (Klein et al., 2016), featured in a preview (Jazayeri and Remington, 2016). This work presents the first successful attempt to selectively target a neuronal population in NHP using optogenetics. It serves as an important first step for cell-specific manipulation of LGN function during binocular vision (Dougherty et al, J Comp Neurol, 2019; Dougherty et al, eNeuro, 2021). A second result of our publication on optogenetics was that retrograde labelling of cortico-geniculate neurons was negligible with this approach. We therefore decided for the next series of experiments to target the projection from V1 to LGN to perform optogenetic injections directly into V1 (Ortiz-Rios et al,bioRxiv,2021). We first used fMRI to measure the global brain activation pattern associated with optogenetic stimulation of V1. The results show very robust local positive BOLD activation at the site of optogenetic stimulation in the V1, and additional remote activation in few connected cortical and subcortical areas (LGN and MT). We also carried out electrophysiological multi-electrode recordings from the different layers in V1 to establish the neurophysiological correlate of the positive BOLD activation that results from optogenetic stimulation. Our results suggest that the positive BOLD signal is best explained by a layer specific V1 spiking activity. In parallel we also performed behavioural tests that demonstrated that V1 optogenetic stimulation can generate an artificial visual percept (‘phosphene’). In the course of this project, we also participated in international collaborations aimed at improving optogenetic methods in NHP before they can be translated for applications in humans (Galvan et al, J Neurosci, 2017; Tremblay et al, Neuron, 2020; Klink et al, Neuroimage, 2021).

In addition to this work on optogenetic stimulation of visual cortex, we also carried out investigations that advanced our understanding on the neuronal basis of attentional sampling and the emergence of theta (3-8 Hz) rhythmic brain activity. In a first publication we demonstrated how interactions between neighbouring neuronal populations at the visual receptive field level give rise to the emergence of theta rhythmic activity that is tightly correlated with attentional sampling (Kienitz, Current Biology, 2018). We then demonstrated in a collaboration the emergence of similar attentional sampling in humans (Chota et al, Scientific Reports, 2018). Comparing theta with gamma oscillations, we could also demonstrate how theta oscillations can serve as a feedforward signal between areas of visual cortex (Kienitz et al, Current Biology, 2021).

Neuroscience involving non-human primates (NHP) requires highest ethical and scientific standards and benefits from a collaborative approach in which resources and methods of good practice are shared in the community, with recent 3R contributions from us for refined implants (Ortiz-Rios et al, J Neurosci Meth, 2018; Perry et al, J Neurosci Meth, 2021) and to the NHP data sharing initiative (Milham et al, Neuron, 2018).

Our work describes the first cell-specific optogenetic targeting visual system circuits (Klein et al, Neuron, 2016). Previous work on optogenetic activation of primary visual cortex (V1) demonstrated the feasibility of the approach to influence behaviour (Jazayeri et al., 2012; Ju et al., 2018). Our work extends this by measuring both the local layer-specific, as well as remote areal brain activation patterns associated with optogenetic stimulation of V1 and to what extent these activation patterns are associated with a visual percept (Ortiz-Rios et al,bioRxiv,2021).

Periodic Reporting for period 4 - OptoVision (Optogenetic investigation of cortical layer-6 neuron contributions to dynamic visual perception)

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