21st Feb: Rich Gardner
Spike timing and phase dynamics in sleep spindle oscillations
In the mammalian forebrain, the state of non-REM sleep is accompanied by an array of neuronal oscillations that span widely different timescales. Some of these oscillations are believed to facilitate the transfer of long-term memory traces from hippocampal region to neocortical areas – a process known as offline ‘systems’ consolidation. Spindle oscillations, which are 0.5-3 second periods of 8-15 Hz activity in the thalamocortical network, are widely believed to play in important role in this process, but precisely how is unknown. During my PhD, I have used tetrode recordings to characterize thalamocortical network activity during spindle oscillations. I found that multiple aspects of thalamic and cortical neuronal firing showed consistent temporal patterns across each spindle epoch, which may explain the stereotyped waxing-waning time course of these oscillations, but could also have bearing on the functional role of spindles in memory processing. I will also briefly talk about my current work, which aims to investigate the specific role that spindles might play in the hippocampus-neocortex dialogue that occurs during sleep after learning.
28th Feb: Laura Atherton
Unravelling the Mechanisms behind Hippocampal Place cell Replay activity in Sharp wave ripples
Sharp wave ripples (SWRs) are a type of oscillation that occur in the hippocampal formation during, for example, periods of slow wave sleep and immobility. During these events, place cell activity which is present in the hippocampus during awake behaviour, tends to be replayed in a time compressed manner. Such activity is believed to facilitate spatial memory consolidation by aiding the transfer of labile spatial memories from the hippocampus to more stable neocortical sites. However it is currently unknown what selects which particular place cells participate, or are active, within a given SWR. Is there a plasticity-dependent bias for certain cells to participate? Are there different intrinsic properties between the participating and non-participating cells? Is there a combination of the two or something else entirely? Unfortunately I can’t answer any of these questions yet, but I will present the work I have been doing during the first year of my PhD to attempt to address the questions, both from an experimental and computational perspective.
7th Mar: Emma Robinson
Emotions, decision-making and depression
Our research group is interested in the pathology of major depressive disorder and its treatment with antidepressants. Despite the fact that the first drug treatments for depression were discovered in the 1950s and we have a detailed understanding of where in the brain they act, we still lack a clear understanding of how these effects relate to the emotional symptoms seen in depression. We have also failed so far to provide an explanation for how or why major depressive disorder develops. In this talk, I will present a novel hypothesis about the cause and treatment of depression and identify some of the challenges we face in trying to test this theory. I will focus on two areas which are of specific interest. The first relates to emotions and decision-making and the second relates to the gene by environment interactions vulnerability to depression.
21st Mar: Innes Cuthill
Animal Camouflage: Evolutionary Biology meets Computational Neuroscience, Art and War
Animal camouflage provides some of the most striking examples of the workings of natural selection; it has also long been an inspiration for military camouflage design, with the pioneers of camouflage theory being both artists and natural historians. While the general benefits of camouflage are obvious, understanding the precise means by which the viewer is fooled represent a challenge. This is because animal camouflage is an adaptation to the eyes and mind of another animal, often with a visual system different from (and sometimes superior to) that of humans. A full understanding of the mechanisms of camouflage therefore requires an interdisciplinary investigation of the perception and cognition of non-human species, involving the collaboration of biologists, neuroscientists, perceptual psychologists and computer scientists. I review the various forms of camouflage from this perspective, illustrated by the recent upsurge of experimental studies of long-held, but largely untested, theories of defensive colouration.
4th Apr: Claudia Clopath
Receptive field formation by interacting excitatory and inhibitory plasticity
Cortical neurons receive a balance of excitatory and inhibitory currents. This E/I balance is thought to be essential for the proper functioning of cortical networks, because it ensures their stability and provides an explanation for the irregular spiking activity observed in vivo. Although the balanced state is a relatively robust dynamical regime of recurrent neural networks, it is not clear how it is maintained in the presence of synaptic plasticity on virtually all synaptic connections in the mammalian brain. We recently suggested that activity-dependent Hebbian plasticity of inhibitory synapses could be a self-organization mechanism by which inhibitory currents can be adjusted to balance their excitatory counterpart (Vogels et al. 2011). The E/I balance not only generates irregular activity, it also changes neural response properties to sensory stimulation. In particular, it can lead to a sharp stimulus tuning in spiking activity although subthreshold inputs are broadly tuned, it can change the neuronal input-output relation and cause pronounced onset activity due to the delay of inhibition with respect to excitation. This control of neuronal output by the interplay of excitation and inhibition suggests that activity-dependent excitatory synaptic plasticity should be sensitive to the E/I balance and should in turn be indirectly controlled by inhibitory plasticity. Because we expected that excitatory plasticity is modulated by inhibitory plasticity, the question under which conditions excitatory Hebbian learning rules can establish receptive fields needs to be re-evaluated in the presence of inhibitory plasticity. In particular, it is of interest under which conditions neurons can simultaneously develop a stimulus selectivity and a cotuning of excitatory and inhibitory inputs. To address these questions, we analyse the dynamical interaction of excitatory and inhibitory Hebbian plasticity. We show analytically that the relative degree of plasticity of the excitatory and inhibitory synapses is an important factor for the learning dynamics. When excitatory plasticity rate is increased with respect to the inhibitory one, the system undergoes a Hopf bifurcation, losing stability. We also find that the stimulus tuning of the inhibitory input neurons also has a strong impact on receptive field formation. When stimulus tuning of the inhibitory input neurons has the same width than the one of the excitatory input neurons, stimulus selectivity is prevented, but if the inhibitory input neurons are not tuned, selectivity emerge. This latter scenario, together with our analysis, suggests that the sliding threshold of BCM rules may not be implemented on a cellular level but rather by plastic inhibition arising from interneurons without stimulus tuning. If the stimulus tuning of the inhibitory input neurons is broader than that of the excitatory inputs, constant with experimental findings, we observe a local BCM behavior that leads to a stimulus selectivity on the spatial scale of the inhibitory tuning width. This work is done in collaboration with Tim Vogels and Henning Sprekeler.