PSL-UCL workshop on sensory systems in complex environments

London, 25-26 June 2015

• INTRODUCTION
  Ian Scott (UCL), Myriam Nechad (PSL), Maria Chait (UCL).
• Joerg Albert
  The Drosophila Antennal Ears as Universal Tools for the Study of Sensory Biology
  The antennal ears of Drosophila are a powerful model system for the molecular dissection of mechanosensation, and specifically of mechanotransduction. Some of the key principles of vertebrate ears, such as e.g. nonlinear compression and amplification, have been demonstrated for fly hearing and numerous genes have been identified that play specific roles within the auditory system. The ears of different Drosophila species differ in their spectral tuning to match differences in the spectral composition of the conspecific courtship songs. The presentation will recapitulate previous findings and highlight ongoing riddles and controversies. Particular effort will be spent on making suggestions as to how the study of the fly's ear can contribute to our general understanding of sensory organ operation, homeostasis and maintenance.
• Pascal Martin
  The hair-cell bundle as a mechanical antenna and amplifier for hearing.
  I will review micromechanical experiments at the level of the cellular microphone of the inner ear - the hair cell - whose function is to transduce sound-evoked vibrations into electrical nervous signals. I will discuss the origin of stiffness and drag of the hair bundle, a tuft of cylindrical protrusions that protrudes from the apical surface of each hair cell, and show how these physical parameters can influence the cell's characteristic frequency of mechanosensitivity. A dynamical interplay between mechanosensitive ion channels, molecular motors, and calcium feedback results in spontaneous oscillations of the hair-cell bundle. Oscillations allow the hair cell to actively resonate with its mechanical input at the expense of nonlinear distortions with properties that are characteristic of auditory perception. Our results promote a general principle of sound detection that is based on nonlinear amplification by self-sustained "critical" oscillators in the inner ear, i.e. active dynamical systems that operate on the brink of an oscillatory instability called a Hopf bifurcation.
• Karim Benchenane
  Explicit memory creation during sleep: a causal role of place cells in navigation
  Hippocampal place cells assemblies are believed to support the cognitive map, and their reactivations during sleep are thought to be involved in spatial memory consolidation. By triggering intracranial rewarding stimulations by place cell spikes during sleep, we induced an explicit memory trace, leading to a goal-directed behavior toward the place field. This demonstrates that place cells' activity during sleep still conveys relevant spatial information and that this activity is functionally significant for navigation.
• Aman Saleem
  Hippocampal representation of spatial decisions in uncertain environments
  I will present recent results regarding the activity of place cells when sensory uncertainty is varied. I recorded extracellular CA1 activity while animals performed a navigation task in a virtual environment, and controlled the sensory uncertainty by varying the visual contrast at which the virtual environment was presented. We find that increasing uncertainty does not change the average firing rate or population spread of activity. However, the population of neurons make more errors at representing the environment with growing uncertainty. Further, the behavioural errors made by the animals are directly correlated with errors in the hippocampal representation.
• German Sumbre
  A neuronal correlate of visual motion perception in the zebrafish optic tectum
  Following coherently moving visual stimuli (conditioning stimulus, CS), many organisms perceive, in the absence of physical stimuli, illusory motion in the opposite direction, an phenomenon known as the motion aftereffect (MAE). Here we use MAE as a tool to study the neuronal mechanisms underlying visual motion perception in zebrafish. Taking advantage of the zebrafish optokinetic response as an indicator of visual motion perception, we showed that zebrafish larva perceives MAE. Optogenetic blockage of eye movements during CS did not prevent the emergence of MAE. Using two-photon calcium imaging of behaving GCaMP3 larvae we found sustained rhythmic activities among direction-selective (DS) tectal neurons that were associated with the perception of MAE. Additionally, CS induced habituation of DS neurons in the CS direction in the tectum but not in the retina. Finally, an empirical mathematical model reproduced the MAE phenomenon suggesting a functional neuronal circuit capable of generating perception of visual motion.
• Mickael Tanter
  fUltrasound: a new neuro-imaging modality
  
• Christian Lorenzi
  Auditory processing of temporal information: Effects of age and cochlear damage
  Over the last decades, a wealth of studies have demonstrated that temporal envelope and temporal fine structure play an important role in speech and music perception. We will review recent behavioral work conducted by our team, aiming to clarify the effects of cochlear damage and ageing on the auditory processing of temporal envelope and temporal fine structure cues, respectively. The results should be help designing better screening tools for ENT clinicians and audiologists, and help improving signal processing for digital hearing aids.
• Stuart Rosen
  Developmental aspects of perceiving speech in 'noise'
  We rarely hear speech in quiet, yet much remains to be learned about how the ability to understand speech in the presence of other sounds develops through childhood. I will review a number of studies comparing children in primary school to young adults in their abilities to understand simple sentences in the presence of various kinds of maskers, mostly consisting of other speech. Perhaps the most striking result is that younger children appear to be much more affected by the presence of background speech than adults are, and this ability is not yet fully developed at the end of primary school (age 11).
• Fred Dick
  Short and long-term learning to optimize - or at least improve - performance in complex auditory environments
  I will discuss some experiments that have aimed at understanding the process and outcome of acquiring expertise in perceiving meaningful sounds in complex auditory environments. We have taken several approaches to this problem, including studying environmental sound and scene perception, as well as examining some of the the mechanisms underlying skilled musical performance and perception. Time and data permitting, I will also discuss some in-progress work on auditory attention to spectrally segregated informational streams.
• Jennifer Linden
  Mind the Gap: Two Dissociable Mechanisms of Temporal Processing in the Auditory System
  High temporal acuity of auditory processing underlies perception of speech and other rapidly varying sounds. A common measure of auditory temporal acuity in humans is the threshold for detection of brief gaps in noise. Gap-detection deficits, observed in developmental disorders, are considered evidence for ``sluggish'' auditory processing. Here we show, in an animal model of developmental disorder, that deficits in auditory brain sensitivity to brief gaps in noise do not imply a general loss of central auditory temporal acuity. Extracellular recordings in three different subdivisions of the auditory thalamus in anaesthetised BXSB/MpJ-Yaa mice revealed a stimulus-specific, subdivision-specific deficit in thalamic sensitivity to brief gaps in noise in experimental animals relative to controls. Neural responses to brief gaps in noise were reduced, but responses to other rapidly changing stimuli unaffected, in lemniscal and non-lemniscal (but not polysensory) subdivisions of the medial geniculate body. Through experiments and modelling, we demonstrate that the observed deficits in thalamic sensitivity to brief gaps in noise arise from reduced neural population activity following noise offsets, but not onsets. These results reveal dissociable sound-onset-sensitive and sound-offset-sensitive channels underlying auditory temporal processing, and suggest that developmental disorders specifically affect the sound-offset-sensitive channel.
• Alan Johnston
  Computing global motion from local signals
  The aperture problem limits the information that can be extracted from a local analysis of image motion. This means information needs to be integrated across space to compute the global motion of objects. We can study this process using Gabor arrays. We show that motion induced position shifts and motion drag is computed after global motion computation and consider a new way to combine the local velocities - the harmonic vector average. Finally I will introduce a new stimulus that shows the visual system considers more complex motion patterns than global translation before it comes to a final resolution of the aperture problem.
• Daniel Pressnitzer
  Adaptive processes for auditory perception.
  I will review two lines of evidence suggesting that auditory perception is strongly modulated by several kinds of adaptive processes. First, using stochastic stimuli to probe auditory memory in human listeners, I will show that past experience with a sound can have a rapid but profound effect on its subsequent processing. Second, I will describe a set of rapid context effects showing that even the most basic of auditory features can be impacted by the prevailing statistics of the acoustic context. Together, these results suggest that auditory processing and auditory learning could be more closely intertwined that usually recognized.
• Maneesh Sahani
  Probabilistic inference in complex environments
  
• Ken Harris's talk at FIL
  Coupling of single neurons to populations in sensory cortex
  The cortex operates through the combined activity of large populations of neurons. These populations show patterns of coordinated activity which, even in primary sensory areas, reflect the interplay of sensory stimuli with patterns the brain produces endogenously. To study the structure of cortical population activity, we applied novel analysis methods to recordings of neuronal populations of auditory and visual cortex. The results reveal that - similarly to systems studied in statistical mechanics - much of the structure of cortical population activity can be quantitatively summarized by a small number of "macroscopic variables", which obey lawful dynamics and are related to the animal's behaviour state.
  4:15pm, Friday 26th June, 4th floor seminar room, WTCN, 12 Queen Square, London WC1N 3BG. FIL Brain Meetings.
• THE FUTURE
  Opportunities for UCL - PSL collaboration
  Chaired by Myriam Nechad (PSL), Lorraine Dardis (UCL).
  This slot is to discuss opportunities for collaboration between UCL and PSL labs, and for the exchange of scientists and students across the Channel. Funding for bilateral collaboration, european projects, etc. Joint studentships and training programmes (masters, PhD, etc.). Bench fees, scholarships, travel grants. What are the converging and complementary scientific interests? And so on...
• STUDENT SESSION
  Chairs: Camille Tardieu, Nihaad Paraouty
  Speakers: Biao Yang, Department of Civil, Environmental and Geomatic Engineering (UCL), Melanie Tobin, Institut Curie (PSL), Huriye Atilgan, Ear Institute (UCL), Hi-Jee Kang, ENS (PSL), Vincent Adam, Gatsby Institute (UCL), Jane Mattley, Ear Institute (UCL), Thomas Andrillon, ENS (PSL).