Medial accessory olivary nucleus asymmetry and its selective degeneration in Parkinson's disease: A human…

Cohort studyClinical neuropathology· Aug 2026

Medial accessory olivary nucleus asymmetry and its selective degeneration in Parkinson's disease: A human neuropathological study.

Tahreem Fatima, Shahzad Shams

NeuropathologyCohort studyQ4IF 0.6

Medial accessory olivary nucleus neuron density is markedly lower in Parkinson's disease.

Medial accessory olivary nucleus asymmetry and its selective degeneration in Parkinson's disease: A human neuropathological study.

Tahreem Fatima, Shahzad Shams

Clinical neuropathology · Aug 2026 · Q4 in Pathology

Background

The medial accessory olivary nucleus (MAO), a distinct but inconsistently present subnucleus of the human inferior olivary complex, is poorly characterized despite its proposed role in cerebellar motor circuitry.

Purpose

We aimed to investigate its structural asymmetry, functional correlates, and pathological vulnerability in humans.

Methods

We performed high-resolution histological analysis (Nissl and immunohistochemistry) in 35 neurologically normal brains to quantify MAO volume and neuronal numerical density and relate these to handedness and lifetime manual dexterity.

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Results

43%

Parkinson's brains had fewer surviving neurons in this nucleus than controls

More results

The MAO was identifiable in 74% (26/35) of neurologically normal cases.

A significant volumetric asymmetry was present (p < 0.01), with larger MAO volume contralateral to the dominant hand, and the asymmetry index correlated with lifetime manual dexterity scores (r = 0.54, p = 0.002).

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Conclusion

The MAO may be a neuroanatomically variable but functionally lateralized structure that appears linked to fine motor control and may exhibit selective vulnerability in PD.

Medial accessory olivary nucleus asymmetry and its selective degeneration in Parkinson's disease: A human neuropathological study.

Medial accessory olivary nucleus asymmetry and its selective degeneration in Parkinson's disease: A human neuropathological study.

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