Inferior olivary

The inferior olive (IO) is a nucleus in the brainstem with neurons that exhibit continuous sub-threshold activity. It provides one of the two main inputs to the cerebellum: the so-called climbing fibers (cf). Activation of the cf is generally thought to be involved in the timing of motor commands and/or motor learning. cf activation triggers large all-or-none action potentials in cerebellar Purkinje cells (PC), which override any ongoing activity and temporarily silence the cells. Empirical evidence indicates that cf can transmit a short burst of spikes following an IO cell somatic spike, potentially increasing the amount of information transferred to the cerebellum with each activation [1]. The default configuration with IO is implemented in io.yaml.

Configuration

In io.yaml , a new region called inferior_olivary was added to the canonical circuit + DCN model (see DCN section for more microcircuit info). This region contains only one Layer Partition: io layer. io layer has a thickness of \(100 \mu m\) . Additionally, to ensure that inferior_olivary are placed under the cerebellar_nuclei, its origin was set to [0, 0, -300].

Cell types

No morphologies are currently available for IO neurons, so they are modelled as point neurons. We considered a single population of IO neurons. The number of IO neurons to be placed is estimated based on the ratio between the number of PC and IO itself, which is reported to be 5:1 in Blatt and Eisenman [2].

Placement

IO neurons are assumed to be uniformly distributed in their own layer, hence the bsb RandomPlacement strategy is chosen to place them.

Connectivity

#	Source Name	Source Branch	Target Name	Target Branch	Strategy	Specifics	References
22	IO	/	PC	/	FixedIndegree	indegree = 1	Geminiani et al. (2024) [3]
23	IO	/	SC	/	ConnectomeIO_MLI	/	Geminiani et al. (2024) [3]
23	IO	/	BC	/	ConnectomeIO_MLI	/	Geminiani et al. (2024) [3]
24	IO	/	DCNp	/	AllToAll	affinity = 0.5	Geminiani et al. (2024) [3]
25	IO	/	DCNi	/	AllToAll	affinity = 0.5	Geminiani et al. (2024) [3]
26	DCNi	/	IO	/	AllToAll	affinity = 0.5	Geminiani et al. (2024) [3]

References

[1]

De Gruijl, J. R., Bazzigaluppi, P., de Jeu, M. T., & De Zeeuw, C. I. (2012). “Climbing fiber burst size and olivary sub-threshold oscillations in a network setting.” PLoS computational biology, 8(12), e1002814. https://doi.org/10.1371/journal.pcbi.1002814

[2]

Blatt, G. J., & Eisenman, L. M. (1985). “A qualitative and quantitative light microscopic study of the inferior olivary complex of normal, reeler, and weaver mutant mice.” Journal of Comparative Neurology, 232(1), 117-128. https://doi.org/10.1002/cne.902320110

[3] (1,2,3,4,5,6)

Geminiani, Alice, et al. “Mesoscale simulations predict the role of synergistic cerebellar plasticity during classical eyeblink conditioning.” PLOS Computational Biology 20.4 (2024): e1011277. https://doi.org/10.1371/journal.pcbi.1011277.