June, 19th – Isabelle Ferezou
Title: A mesoscopic view of tactile sensory information processing in the cerebral cortex
Abstract: Since the first description of its remarkable cellular organization by Woolsey and Van der Loos (1970), the whiskers representation in the rodent primary somatosensory cortex (S1) has become a major model for studying the cortical processing of tactile sensory information. In its layer 4, neurons form clusters, called barrels, that share the same topology as the whiskers on the snout of the animal, each neuronal column associated with a barrel receiving primarily inputs coming from its corresponding whisker.
A huge amount of information has been collected over the past 50 years on the whiskers sensory system; however it is still largely unknown how it really integrates distributed information to build a global percept of the tactile scene. Working at a mesoscopic scale that allows visualizing how the information flows throughout cortical columns and further propagates to other cortical areas is a real asset to address this question. Voltage sensitive dye imaging, which benefits from a sub-columnar spatial resolution and a millisecond time resolution reveals how, upon tactile stimulation of a given whisker, information is rapidly transmitted to its corresponding column in S1, but also, within the next couple of milliseconds, to the secondary somatosensory cortex and then to the primary motor cortex. Using this method, we described with an unprecedented precision the topography of whiskers representation, as well as the lateral propagation of sensory inputs within these cortical areas, thus providing insights in the neuronal dynamics at play for integration of complex multi-whisker inputs in the cortical network.
June, 12th – Pradeep Dheerendra
Title: Dynamics underlying auditory object boundary detection and segregation
Abstract: A visual object might be easy to define and understand, but objects perceived via audition are also important. Auditory object analysis involves the process of detecting, segregating and representing spectro-temporal regularities in the acoustic environment into stable perceptual units. Thus the auditory system accomplishes the process of transformation of acoustic waveform into an object based representation. This talk focuses on two fundamental aspects of auditory object processing viz. detection of auditory object boundary and auditory segregation. In the first study, I present the dynamics underlying the detection of emergence of a new auditory object in an ongoing auditory scene using MEG. I found a slow drift signal at the object boundary which I think might be the precision signal. In the second study, I present the brain basis underlying human auditory figure-ground analysis in a macaque model using fMRI and psychophysics. This has provided spatial priors for macaque neurophysiology.
June, 5th – Alex Cayco Gajic
Title: High-dimensional representations in cerebellar granule cells
Abstract: The cerebellum is thought to learn sensorimotor relationships to coordinate movement. Sensory and motor information is sent to a large number of cerebellar granule cells, which comprise the vast majority of neurons in the brain. Theoretically, this large anatomical expansion is thought to help pattern separation by representing sensorimotor information in a high-dimensional granule cell population code. However, how the granule cell population activity encodes sensory and motor information, and whether granule cell populations can support high-dimensional representations, is poorly understood. To address this, we used a high-speed random-access 3D 2-photon microscope to simultaneously monitor the Ca2+ activity in hundreds of granule cell axons of spontaneously behaving animals. We find that granule cell population activity transitions between separate, orthogonal coding spaces representing periods of quiet wakefulness vs. active movement, and that the granule cell representation is higher dimensional than has previously been observed.
May, 29th – Lucia Prieto Godino
Title: Evolution of olfactory systems on the fly
Abstract: Sensory systems encode the world around us to guide context-dependent appropriate behaviours that are often species-specific. This must involve evolutionary changes in the way that sensory systems extract environmental features and/or in the downstream sensory-motor transformations implemented. However, we still know little about how evolution shapes neural circuits. We are studying the olfactory system of Drosophila and tsetse flies across multiple species spanning a wide range of ecological niches and divergence times. We find divergent odour-guided behaviour towards host odours. To elucidate the cellular, circuit and molecular basis behind this behavioural evolution we are employing a multidisciplinary approach, including field work, the development of genetic tools across species, calcium imaging, single cell transcriptomics and reconstruction of central olfactory circuits at synaptic resolution. I will discuss the progress we have made in our efforts to understand how evolution tinkers neural circuits as animals adapt to different environments.
May, 22nd – Bradley Love
Title: A clustering account of spatial and non-spatial concept learning
Abstract: How do we learn to categorise novel items and what is the brain basis of these acts? For example, after a child is told an animal is a dog, how does that experience shape how she classifies future items? I will present model-based fMRI results concerning how people learn categories from examples and touch on parallel findings with monkey single-unit recordings. Our analyses indicate that the medial temporal lobe (MTL), including the hippocampus, plays an important role in both learning and recognition. Successful cognitive models, which explain both behavioural and brain measures, learn to selectively weight (i.e., attend) to stimulus aspects that are task relevant. This form of weighting, or top-down attention, can be viewed as a compression process. I will discuss how the medial prefrontal cortex (mPFC) and the hippocampus coordinate to build low-dimensional representations of learned concepts, as well as how the dimensionality of visual representations along the ventral stream is altered by the learning task. Finally, this general learning mechanism offers a straightforward account of spatial learning, including place and grid cell activity in both human and rodent studies.
May, 15th – Grace Lindsay
Title: Modelling the influence of feedback in the visual system
Abstract: Cortico-cortical feedback is common in the visual system and is believed to be involved in processes such as perceptual inference, attention, and learning. In this talk I will demonstrate how convolutional neural networks can be used to explore how such feedback works. In the first half of the talk, I will focus on the signals from prefrontal areas that are believed to control top-down feature attention. In the second half, I’ll discuss ongoing work on how local feedback connections help process noisy images.
May, 8th – bank holiday
May, 1st –
April, 24th –
April, 17th – Easter
April, 10th – Bank holiday
April, 3rd – Timothy O’Leary
March, 27th – Silvia Maggi