Seminars

When listening to music, we typically lock onto and move to a beat (1-6 Hz). Behavioral studies on such synchronization (Repp 2005) abound, yet the neural mechanisms remain poorly understood. Some models hypothesize an array of self-sustaining entrainable neural oscillators that resonate when forced with rhythmic stimuli (Large et al. 2010). In contrast, our formulation focuses on event time estimation and plasticity: a neuronal beat generator that adapts its intrinsic frequency and phase to match the extermal rhythm. The model quickly learns new rhythms, within a few cycles as found in human behavior. When the stimulus is removed the beat generator continues to produce the learned rhythm in accordance with a synchronization continuation task.

Interpretation of interval timing data generated from animal models is complicated by ostensible motivational effects which arise from the delay-to-reward imposed by interval timing tasks, as well as overlap between timed and non-timed responses. These factors become increasingly prevalent at longer intervals. To address these concerns, two adjustments to long interval timing tasks are proposed. First, subjects should be afforded with reinforced non-timing behaviors concurrent with timing. Second, subjects should initiate the onset of timed stimuli. Under these conditions, interference by extraneous behavior would be detected in the rate of concurrent non- timing behaviors, and changes in motivation would be detected in the rate at which timed stimuli are initiated. In a task with these characteristics, rats initiated a concurrent fixed-interval (FI) random-ratio (RR) schedule of reinforcement. This design facilitated response-initiated timing behavior, even at increasingly long delays. Pre-feeding manipulations revealed an effect on the number of initiated trials, but not on the timing peak function.

Exerting controlled forces in a non-contact way is important in biomedical investigations which require holding, moving, or mechanically probing biomedical samples. Optical and acoustic manipulation of microscopic samples both play a prominent role among suitable technologies. The differences in the physical laws and in the typical length scales governing acoustic and optical forces make them complementary: Acoustic forces can levitate large and heavy particles, which optical tweezers could not handle without adverse high-power effects, while optical forces cover subcellular scales. The talk will contrast the two modalities, and identify situations where one or the other is favorable, or when a combination of both is the best choice.

The subdivision benefit refers to the positive effect of subdividing a beat on sensorimotor synchronization. We recorded electroencephalograms of musicians and non-musicians to study how they listened or finger-tapped to a beat, subdivided into four distinct subdivisions. Musicians showed more consistent tapping responses than non-musicians, and enhanced neural entrainment during the tapping task than in the listening task. In both groups, there was a neural enhancement of the beat frequency and its first harmonic (related to duplets) after listening to the four subdivisions. Furthermore, non-musicians tapped more consistently to the beat of duplets than other subdivisions. Altogether, this suggests a neural and behavioral advantage for binary subdivisions, that can be modulated with formal training in music.

Pain is a major clinical problem affecting 1 in 5 people in the world. There are unresolved questions that urgently require answers to treat pain effectively, a crucial one being how the feeling of pain arises from brain activity. Computational models of pain consider how the brain processes noxious information and allow mapping neural circuits and networks to cognition and behaviour. To date, they have generally have assumed two largely independent processes: perceptual and/or predictive inference, typically modelled as an approximate Bayesian process, and action control, typically modelled as a reinforcement learning process. However, inference and control are intertwined in complex ways, challenging the clarity of this distinction. I will discuss how they may comprise a parallel hierarchical architecture that combines pain inference, information-seeking, and adaptive value-based control. Finally, I will discuss whether and how these learning processes might contribute to chronic pain.

Threshold-linear networks (TLNs) display a wide variety of nonlinear dynamics including multistability, limit cycles, quasiperiodic attractors, and chaos. Over the past few years, we have developed a detailed mathematical theory relating stable and unstable fixed points of TLNs to graph-theoretic properties of the underlying network. In particular, we have discovered that a special type of unstable fixed points, corresponding to "core motifs," are predictive of dynamic attractors. Recently, we have used these ideas to classify dynamic attractors in a two-parameter family of inhibition-dominated TLNs spanning all 9608 directed graphs of size n=5. Remarkably, we find a striking modularity in the dynamic attractors, with identical or near-identical attractors arising in networks that are otherwise dynamically inequivalent. This suggests that, just as one can store multiple static patterns as stable fixed points in a Hopfield model, a variety of dynamic attractors can also be embedded in a TLN in a modular fashion.

Gravity is a constant in our lives. It provides an internalized reference to which all other perceptions are related. We can experimentally manipulate the relationship between physical gravity with other cues to the direction of “up” using virtual reality - with either HMDs or specially built tilting environments - to explore how gravity contributes to perceptual judgements. The effect of gravity can also be cancelled by running experiments on the International Space Station in low Earth orbit. Changing orientation relative to gravity - or even just perceived orientation – affects your perception of how far away things are (they appear closer when supine or prone). Cancelling gravity altogether has a similar effect. Changing orientation also affects how much visual motion is needed to perceive a particular travel distance (you need less when supine or prone). Adapting to zero gravity has the opposite effect (you need more). These results will be discussed in terms of their practical consequences and the multisensory processes involved, in particular the response to visual-vestibular conflict.

Each spring, billions of Bogong moths escape hot conditions in different regions of southeast Australia by migrating over 1000 km to a limited number of cool caves in the Australian Alps, historically used for aestivating over the summer. At the beginning of autumn the same individuals make a return migration to their breeding grounds to reproduce and die. To steer migration Bogong moths sense the Earth’s magnetic field and correlate its directional information with visual cues. In this presentation, we will show that a critically important visual cue is the distribution of starlight within the austral night sky. By tethering spring and autumn migratory moths in a flight simulator, we found that under natural dorsally-projected night skies, and in a nulled magnetic field (disabling the magnetic sense), moths flew in their seasonally appropriate migratory directions, turning in the opposite direction when the night sky was rotated 180°. Visual interneurons in the moth’s optic lobe and central brain responded vigorously to identical sky rotations. Migrating Bogong moths thus use the starry night sky as a true compass to distinguish geographic cardinal directions, the first invertebrate known to do so. These stellar cues are likely reinforced by the Earth’s magnetic field to create a robust compass mechanism for long-distance nocturnal navigation.

In the Learning Salon, we will discuss the similarities and differences between biological and machine learning, including individuals with diverse perspectives and backgrounds, so we can all learn from one another.

Ultra-low-cost, easily implemented and flexible two-photon scanning microscopy modification offering a several-fold expanded three-dimensional field of view that also maintains single-cell resolution. Application of our system for imaging neuronal activity has been demonstrated on mice, zebrafish and fruit flies. Website: https://github.com/BadenLab/nTCscope

Mahzarin Banaji and her colleague coined the term “implicit bias” in the mid-1990s to refer to behavior that occurs without conscious awareness. Today, Professor Banaji is Cabot Professor of Social Ethics in the Department of Psychology at Harvard University, a member of the American Academy of Arts and Sciences, the National Academy of Sciences and has received numerous awards for her scientific contributions. The purpose of the seminar, Blindspot: Hidden Biases of Good People, is to reveal the surprising and even perplexing ways in which we make errors in assessing and evaluating others when we recruit and hire, onboard and promote, lead teams, undertake succession planning, and work on behalf of our clients or the public we serve. It is Professor Banaji’s belief that people intend well and that the inconsistency we see, between values and behavior, comes from a lack of awareness. But because implicit bias is pervasive, we must rely on scientific evidence to “outsmart” our minds. If we do so, we will be more likely to reach the life goals we have chosen for ourselves and to serve better the organizations for which we work.

The study of altered states of consciousness has long had the potential to provide important insight into the nature of consciousness. In recent years there has been a resurgence of research and public interest in atypical or altered states of consciousness. These have focused both on conditions in which consciousness is considered to be impaired due to brain trauma or enhanced in some way through mediation practices or ingestion of psychedelics. The talk will begin with a brief overview of recent scientific approaches to understanding these different types of altered consciousness. The remainder of the talk will focus on lab-based experiments conducted by myself and others looking at the effects of serotoninergic hallucinogens (i.e. psilocybin and LSD) on perceptual and cognitive function. Together this body of research provides important new insights for the scientific study of consciousness and an initial understanding of the neuropharmacological mechanisms underlying conscious experience.