We are interested in how brains process sensory information and produce behaviours.
To effectively acquire and process information in complex and constantly-changing environments, brains must themselves be dynamic and operate on many different time scales. Neural dynamics arise from processes occurring at many levels, from network feedback interactions, to the sub-cellular processes involved in synaptic plasticity. Our goal is to understand how the brain uses these processes to encode and interpret sensory information, whether that is to produce a specific behaviour or to store the information as a memory.
By looking to nature for sensing experts, we can gain insight into the general mechanisms of neuronal information processing. The weakly electric fish is particularly well-suited for these studies. These fish have evolved an exquisite electric sense that enables them to capture prey and communicate in dark and murky waters. While the brain structures involved in the electric sense are relatively simple, they exhibit many similarities with our own sensory systems.
Our studies are multidisciplinary, using techniques ranging from cellular electrophysiology to computational modeling and behavioural analyses. Such a comprehensive and integrative approach will play an essential role in understanding the complex issues underlying information processing in the brain.
Dynamic neural processing in weakly electric fish
We are studying a sense that is foreign to us - the "electric sense" of the weakly electric fish. These fish generate an oscillating high-frequency electric field surrounding their bodies. Objects in the environment perturb this electric field; the fish sense these perturbations using specialized electroreceptors distributed on their entire body surface. Electric fish inhabit dark and murky waters and cannot rely on visual cues, and so the electric sense plays a key role in prey capture and navigation. In addition, these fish produce precise modulations in their electric discharge to communicate with conspecifics.
Electric fish must overcome significant challenges to sense with electric fields. One is that the distortions produced by objects are not only very small, but are contaminated by many sources of noise. Another is that these fish must use a 2-dimensional sensory signal (from their skin-surface electroreceptors) to infer the goings-on in their 3-dimensional world. Despite such challenges, these fish can reliably capture very small prey and effectively interact with conspecifics. How do they perform these exquisite behaviors? What are the neural mechanisms for adapting to their changing environments and filtering out the many noise sources? How do these fish extract 3D information from 2D electrosensory signals? How do they deal with the high energetic costs of generating their electric field? We're beginning to tackle these issues and finding that despite the exotic nature of the electric sense, there are some interesting parallels with our own visual and auditory systems.
Our research projects focus on various aspects of electrosensory processing:
1. The physics of the electric field and the features of dynamic electrosensory stimuli. We are using finite-element methods to study the physical basis of the electric field and gain insight into natural electrosensory stimuli. We use behavioural methods to investigate perceptual limits and elucidate the salient features of electrosensory stimuli. From this work, we hope to gain insight that will help determine the codes for electrosensory perception.
2. Production of the electric organ discharge. We are using electrophysiology and computational modeling to study the energetic costs and biophysical mechanisms underlying the control of the electric organ discharge (EOD). The EOD is known to be one of the most precise of all biological oscillators, yet it is behaviourally modulated on millisecond timescales for electrocommunication. How is this balance between precision and flexibility achieved?
3. Encoding of electrosensory information by neurons in early electrosensory pathways. We are using brain slice preparations to explore the role of synaptic plasticity and neuronal feedback in the control of single neuron dynamics. We are also using real-time dynamic-clamp and computational modelling to investigate the role of dynamics and feedback in tuning the response of neural populations to moving objects.