Biology subjects

Touboul, J. D.

Publications and source records attributed to Touboul, J. D..

3 recordsLinked to original sources

bioRxiv2025

Functional architecture for speed tuning in primary visual cortex of carnivores

Perception of motion critically depends on detecting the speed and direction of moving stimuli. The primary visual cortex (V1) of some mammals, including primates and carnivores, exhibits functional organization for key receptive field properties such as orientation, direction, and spatial frequency; however, less is known about the organization of speed-tuned cells. While individual V1 neurons have been shown to exhibit speed selectivity, functional architecture for speed preference has been primarily reported in higher cortical areas such as primate area MT. Using multi-channel electrophysiology in anesthetized female ferrets, we investigated the joint tuning of V1 neurons for spatial frequency, temporal frequency, orientation/direction, and speed. We found significant clustering of cells tuned for speed and for speed preference within single electrode penetrations. We found that both simple and complex cells can exhibit speed tuning, and no strong variation across cortical layers. In reanalysis of intrinsic signal imaging data from cat V1, we observed repeating "hot spots" of high speed selectivity separated by "cold spots" with low tuning for speed. These findings indicate that a functional architecture for speed tuning is present within V1 itself and transmitted to downstream cortical regions. Significance StatementTo perceive moving objects, the visual system must detect both their direction and speed. The primary visual cortex, the first cerebral visual area to receive visual information from the retina via the lateral geniculate nucleus, plays a key role in this process. Here, we demonstrate that the primary visual cortex in carnivores contains speed-tuned neurons. Moreover, these neurons are organized into clustered "hot spots" that repeat across the cortical surface, suggesting a functional architecture for speed. While speed-tuned functional maps were previously thought to exist only in higher visual areas, such as area MT in primates, our findings reveal their presence at the level of primary visual cortex.

neuroscience↗

bioRxiv2024

Latent encoding of movement in primary visual cortex

Neurons in the primary visual cortex (V1) are classically thought to encode spatial features of visual stimuli through simple population codes: each neuron exhibits a preferred orientation and preferred spatial frequency, both of which remaining invariant to other aspects of the visual stimulus. Here, we show that this simple rule does not apply to the representation of major features of stimulus motion, including stimulus direction and temporal frequency (TF). We collected an extensive dataset of cat (of either sex) V1 responses to stimuli covarying in orientation, direction, spatial frequency, and TF to assess the extent of motion selectivity. We show that preferred TF is mostly uniform across the cortical surface. Yet, in over half of V1, the preferred direction is reversed with changing stimulus TF, revealing four distinct map motifs embedded in V1s functional architecture. Similarly, despite the lack of spatial modulation for the preferred TF map and the lack of invariance for the preferred direction map, we found using convolutional neural networks that direction, TF and stimulus speed can be accurately decoded from V1 responses at all cortical locations. These findings suggest that subtle modulations of V1 activity may convey fine information about stimulus motion, pointing to a novel primary sensory encoding mechanism despite complex co-variation of responses to multiple attributes across V1 neurons. Significance StatementUnderstanding how the external world is represented in the brain has long been a central endeavor in neuroscience. In the mammalian primary visual cortex (V1), groups of neurons encode stimulus properties through changes in activity, with "preferred" stimuli eliciting maximal responses, as demonstrated for orientation and spatial frequency. Using an extensive dataset of neuronal responses, we investigated whether V1 also encodes motion speed. We found that cortical response organization remains largely invariant, with neurons exhibiting a uniform preference for temporal frequency. Yet, machine learning algorithms decode motion speed with remarkable precision, revealing that subtle, spatially distributed modulations of activity underlie speed encoding. Moreover, we show that preferred direction flips with speed across 80% of cortex, uncovering a novel co-organization of motion and direction information in V1.

neuroscience↗

bioRxiv2024

Striatal endocannabinoid-long-term potentiation mediates one-shot learning

One-shot learning, the ability to form memories after a single, brief salient event, is essential to adapt ones behaviour in a dynamic world. However, how one-shot learning unfolds in the brain remains unknown. Challenges to elucidate its neural underpinnings stem experimentally from the scarcity of behavioral assays recapitulating one-shot learning in the laboratory, and conceptually from the limited number of neuronal plasticity mechanisms that could support learning after a small number of action potentials, as is common during a one-shot experience. Here, we overcome these challenges and identify a new mechanism for one-shot learning in dorsal striatum that relies on a non-classical form of plasticity, the endocannabinoid-mediated long-term potentiation (eCB-LTP). To do so, we develop a novel one-shot behavioral test, in which mice learn to avoid a sticky tape after a single, spontaneous and brief contact with the uncomfortable substrate, and maintain this memory for more than one month. We use the sticky tape avoidance test to demonstrate that striatal LTP emerges in vivo after one-shot learning; the observed patterns of activity in vivo suggest that eCB-LTP mediates one-shot learning, which we corroborate both ex vivo and through computational modeling. Consistent with this hypothesis, conditional knock-out mice abolishing eCB-LTP show impaired one-shot learning. These results highlight the importance of non-classical plasticity mechanisms in supporting memory formation after a single brief experience.

neuroscience↗