The price of being awake and the function of sleep: synaptic homeostasis

Monday 10 December, 4pm at the Large Lecture Theatre, DPAG/Le Gros Clark Bldg

 

The Cortex Club is delighted to co-host, together with the CNCB, Prof Chiara Cirelli from the University of Wisconsin-Madison, who will be talking to us about her research on synaptic homeostastis during sleep. Please join us on December 10th at the Large Lecture Theatre, located in the Le Gros Clark Building of the Department of Physiology, Anatomy and Genetics.

Prof. Chiara Cirelli has kindly agreed to meet students and staff individually. If you would like to arrange a meeting please contact Fiona Woods (fiona.woods – at – cncb.ox.ac.uk).

 

To join us in the pub after the talk – where we’ll be joined by both Prof Cirelli and Prof Tononi – please register at https://goo.gl/forms/yxneVL15Nxs3YIDG3

 

Abstract
Sleep is universal, tightly regulated, and many cognitive functions are impaired if we do not sleep. But
why? Any hypothesis about the essential function of sleep must take into account that when asleep we
are essentially offline: sensory disconnection must be crucial for whatever function sleep serves. If not,
natural selection would likely have found a way to perform the same function while awake, avoiding
the danger of being unable to monitor the environment.

Over the past 20 years, we have developed and tested a comprehensive hypothesis about the core
function of sleep: The Synaptic Homeostasis Hypothesis (SHY). SHY states that sleep is the price we pay
for brain plasticity. During wakefulness the excitatory synapses that allow neurons to communicate
with each other undergo net potentiation as a result of learning, an ongoing process that happens all the
time while we are awake, constantly adapting to an ever-changing environment. The plasticity of the
brain is essential for survival but is also a costly process, because stronger synapses increase the
demand for energy and cellular supplies, lead to decreases in signal-to-noise ratios, and saturate the
ability to learn. According to SHY, the renormalization of synaptic strength should mainly occur
during sleep when the brain is disconnected from the environment and neural circuits can be broadly
reactivated off-line to undergo a systematic and yet specific synaptic down-selection. This
renormalization favors memory consolidation and the integration of new with old memories, and
eliminates the synapses that contribute more to the “noise” than to the “signal.” Just as crucially,
synaptic renormalization during sleep restores the homeostasis of energy and cellular supplies,
including many proteins and lipids that are part of the synapses, with beneficial effects at both the
systems and cellular level.

I will discuss the rationale underlying this hypothesis and summarize electrophysiological, molecular
and ultrastructural studies in flies, rodents and humans that confirmed SHY’s main predictions,
including the recent observation, obtained using serial block face scanning electron microscopy, that
most synapses in mouse primary motor and sensory cortices grow after wake and shrink after sleep. I
will then present unpublished ultrastructural data obtained in the hippocampus and in the cortex of
mouse pups. Finally, I will examine recent studies by other groups showing the causal role of cortical
slow waves and hippocampal ripples in sleep-dependent synaptic down-selection, and some of the
molecular mechanisms that can mediate this process.

Brain-scale neural circuits for visual motion processing in zebrafish

Wednesday 5 December, 4pm at the Sherrington Library, DPAG/Le Gros Clark Bld

 

 

The Cortex Club is excited to host A. Prof Eva Naumann from the Duke University, who will be talking to us about her research on how neural circuits across the entire brain guide behaviour in zebrafish. Please join us on December 5th at the Sherrington Library, located in the Sherrington Building of the Department of Physiology, Anatomy and Genetics.

Prof. Eva Naumann has kindly agreed to meet students and staff individually. If you would like to arrange a meeting please contact Tai-Ying Lee at tai-ying.lee [at] dpag.ox.ac.uk.

Please join us at the pub after the talk, register at https://goo.gl/forms/OHwnmWPegKVnVRg23

 

Abstract

The larval zebrafish presents an exciting opportunity to investigate the neural basis of vertebrate behavior at the brain scale.  However, it has been particularly difficult to distill neural circuits from whole-brain measurements of neural activity. By combining detailed psychophysics, anatomy, cellular resolution whole-brain imaging, and circuit perturbations, we establish critical links between brain- and circuit-level descriptions of the zebrafish optomotor response. Specifically, we find diverse neural response types distributed across multiple brain regions and show that to transform visual motion into action, these regions sequentially integrate eye- and direction-specific sensory streams, refine representations via interhemispheric inhibition, and demix locomotor instructions into distinct motor modules. Ultimately, we develop a quantitative whole-brain model that explains the behavior and reduces the space of possible synaptic connections into a few critical dimensions of functional connectivity among identified neural response types. More generally, our methodology illustrates a flexible paradigm for studying diverse brain-scale computations related to individuality and motivational states.

Is Brain Surgery Difficult?

Monday 26 November – 5pm at the Swire Seminar Room, University College

 

The Cortex Club is delighted to co-host, together with the University College Science Society, Dr Henry Mash, who will be talking to us about his life as a neurosurgeon.

 

Please join us on November 26th at the Swire Seminar Room, located at University College.

 

 

Dr. Marsh is a now retired, leading neurosurgeon and author of “Admissions: Life as a brain surgeon”; and his memoir “Do No Harm”. Dr Marsh graduated from University College Oxford studying PPE, 1969, and has since went on to revolutionize neurosurgery in the UK and Ukraine. Dr. Marsh will share with us his experiences from his medical career and take us on a journey to see what challenges he has faced.

Seeing depth with two eyes: the binocular physiology of 3D space

Friday 23 November – 1pm at the Large Lecture Theatre, DPAG/Sherrington Bldg

 

As part of DPAG’s Head of the Department Seminar Series, the annual GL Brown Lecture, hosted by the Physiological Society Oxford, is given by Prof Andrew Parker from the University of Oxford, who will be talking to us binocular vision. Please join us on November 23nd at the Large Lecture Theatre, located in the Sherrington Building of the Department of Physiology, Anatomy and Genetics.

 

After the talk, the Cortex Club is hosting a Q&A with Prof Parker.

We would like to encourage students and postdocs in particular to join us 2pm in the Sherrington Library to meet Prof Parker over lunch. We’d be grateful if you could indicate your interest at: https://goo.gl/forms/g6SDsuRVaPhNz6kD2

 

 

Abstract
Neurons that are specifically tuned to binocular depth were discovered in seminal work published 50 years ago by Horace Barlow, Colin Blakemore and Jack Pettigrew in the Journal of Physiology. Their study in the primary visual cortex opened up the era of understanding the physiology of 3-D perception. Thanks to more recent work, we now know that large areas of the extrastriate visual cortex are involved. Sites where binocular stereoscopic depth is integrated with other visual information can be identified and physiological signals related to active perceptual decisions about depth can be isolated. At some sites, a causal role of physiological signals for the perception of depth can be demonstrated by showing that weak electrical microstimulation of the cortex can alter behavioural reports of depth perception. However, there seems to be no single brain module that is responsible for computing stereoscopic depth. This lecture will trace these paths of discovery in human and animal studies. Andrew Parker will show how a better understanding of the physiology of depth perception changes our view of how the brain constructs a representation of the space around us. Findings from this neurophysiological research have implications for the growing popularity of 3-D cinema and immersive virtual reality.

The neural fingerprints of the missing hand

Thursday 22 November – 4pm at the Sherrington Library, DPAG/Sherrington Bldg

 

The Cortex Club proudly presents Associate Prof Dr Tamar Makin from University College London, who will be talking to us brain reorganisation after limb amputation. Please join us on November 22nd at the Sherrington Library, located in the Sherrington Building of the Department of Physiology, Anatomy and Genetics.

 

Dr Tamar Makin has kindly agreed to meet students and staff individually. If you would like to arrange a meeting please contact Paula Kaanders (paula.kaanders -at- wadham.ox.ac.uk).

 

To join us at the pub after the talk please register at https://goo.gl/forms/FgicG7m3kBrmvhUd2

Abstract
Following arm-amputation, brain areas that previously operated the hand will be freed-up, and could potentially be “recruited” to work for other body parts (brain reorganisation). I will present recent results and ideas about how the brain undergoes reorganisation due to hand loss and the need to pick up alternative behavioural strategies. I will explore the neural correlates of a range of alternative hand functions,  including extraordinarily dexterous foot usage, artificial limbs and supernumerary robotic fingers. Based on these findings I will challenge some of the basic textbook assumptions about the triggers and barriers of brain reorganisation, and suggest an alternative framework.