The dialectic of Hebb and homeostasis

Abstract

One contribution of 16 to a discussion meeting issue 'Integrating Hebbian and homeostatic plasticity'. It has become widely accepted that homeostatic and Hebbian plasticity mechanisms work hand in glove to refine neural circuit function. Nonetheless, our understanding of how these fundamentally distinct forms of plasticity compliment (and under some circumstances interfere with) each other remains rudimentary. Here, I describe some of the recent progress of the field, as well as some of the deep puzzles that remain. These include unravelling the spatial and temporal scales of different homeostatic and Hebbian mechanisms, determining which aspects of network function are under homeostatic control, and understanding when and how homeostatic and Hebbian mechanisms must be segregated within neural circuits to prevent interference.This article is part of the themed issue 'Integrating Hebbian and homeostatic plasticity'.

Integrating Hebbian and homeostatic plasticity: the current state of the field and future research directions

“…Many studies have confirmed this original result in vitro [6], as well as ex vivo in acute slices prepared from both juvenile and adult animals that had previously undergone in vivo deprivation [7][8][9][10][11][12][13][14]. Synaptic scaling does have layer-specific properties in cortex, where scaling in layer 4 is limited to early development [7], but layer 5 [12,15] and layer 2/3 [10] can scale throughout adulthood.…”

“…Changing the activity of inhibitory neurons provides an important homeostatic mechanism by which activity levels can be rapidly (within seconds) adjusted through the increase or the decrease in the firing rate of inhibitory neurons to prevent short-term increases in activity levels that would be associated with pathological activity such as seizures; however, recent work suggests that minimizing changes to inhibition helps maintain temporal coding in the network, which is shaped by the inhibitory circuit [37], so some maintenance of inhibitory tone is likely essential for the circuit. Adjusting synaptic strength or neuronal excitability occurs over much longer time courses of hours [6], which would be much too slow to account for activity peaks that would potentially cause pathological over-excitation.…”

“…An important feature of these Hebbian mechanisms in relation to their interaction with homeostatic mechanisms is that their time courses and effects can be wildly different. Hebbian mechanisms are synapse specific and can be implemented over milliseconds (short-term plasticity) to hours (long-term LTP/LTD), whereas synaptic scaling occurs cell-wide and can take a few days to commence in vivo [6,15,16,67]. Hence, there is a considerable disparity between the effects and time courses between these homeostatic and Hebbian mechanisms.…”

Degeneracy in hippocampal physiology and plasticity

“…However, there are several lines of theoretical and experimental evidence, spanning several synaptic and intrinsic components as candidate mechanisms, for concurrent emergence of encoding, stability and activity homeostasis. These lines of evidence also argue for significant advantages when encoding, homeostasis and stability mechanisms are concurrent (Anirudhan and Narayanan, 2015;Honnuraiah and Narayanan, 2013;Ibata et al, 2008;Johnston and Narayanan, 2008;Johnston, 2007, 2010;Nelson and Turrigiano, 2008;Triesch, 2007;Turrigiano, 2011;Turrigiano, 2008Turrigiano, , 2017Zenke et al, 2017).…”

“…http://dx.doi.org/10.1101/203943 doi: bioRxiv preprint first posted online Oct. 16, 2017;Turrigiano, 1999Turrigiano, , 2008Turrigiano, , 2017Turrigiano and Nelson, 2000;van Rossum et al, 2000;Zenke et al, 2017). A prominent theme that spans several such stability theories is metaplasticity (Abraham, 2008;Abraham and Bear, 1996;Abraham and Tate, 1997;Hulme et al, 2013), where the profile of plasticity concomitantly changes with the induction of plasticity (Fig.…”