Sussex Neuroscience

Professor Leon Lagnado


Visual processing: synapses and circuits

Background: Our work exploits the fact that the visual system provides an excellent context in which to study how neural circuits process information: we can control the input to the circuit (light) while observing the activity of neurons and synapses within it. We do this by using multiphoton microscopy to image the activity of fluorescent reporter proteins expressed in the retina and brain of live zebrafish.  This approach has allowed us to analyse how excitatory and inhibitory neurons within the retinal network and the brain contribute to basic computations underlying vision, such as the detection of motion or the orientation of a spatial feature.     

Several projects are possible depending on the PhD students strengths and interests.  Examples include:

Adaptation: We would like to understand the  plasticity of the retinal circuit – changes in the way that visual stimuli are processed according to the recent history of activity.  Changes in the properties of synapses within the retina play a key role in such network plasticity and these changes can in turn be caused by the release of neuromodulators such as dopamine, somatostatin or Substance P.  We will ask how these substances modify the synaptic transmission of the visual signal through the retinal network and how they alter the signals that the retina transmits back to the brain.

Synaptic coding: The first stages of vision and hearing operate with analogue voltage signals but it is unclear how these are recoded for synaptic transmission.  By imaging the release of glutamate we found that ribbon synapses of retinal bipolar cells encode contrast through changes in both the frequency and, unexpectedly, the amplitude of release events.  Higher contrasts cause multiple vesicles to be released within an event, and such coding by amplitude often continues after the rate code has reached a maximum frequency. We would like to understand the potential advantages of this amplitude code and whether it operates in other parts of the visusl system. 

Selected publications

(For full list of publications and more details about the lab, please visit:

James, B Darnet L, Moya-Diaz J, Seibel S-H, Lagnado L. (2019). An amplitude code transmits information at a visual synapse.  Nature Neuroscience (In Press).

Johnston, J., Seibel, S-H., Darnet, L., Renninger, S., Orger, M. & Lagnado, L. (2019).  A Retinal Circuit Generating a Dynamic Predictive Code for Oriented Features.  Neuron DOI:

Rosa JM, Ruehle S, Ding H, Lagnado L. (2016). Crossover Inhibition Generates Sustained Visual Responses in the Inner Retina. Neuron, 90(2):308-19. 

Lagnado, L. & Schmitz, F. (2015).  Ribbon synapses and visual processing in the retina.  Annual Reviews of Vision Science, 1:235-262. 

Nikolaev, A., B. Odermatt, Leung, K.-M. and L. Lagnado. (2013). Synaptic mechanisms of adaptation and sensitization in the retina.   Nature Neuroscience, 7:934-4171.