Objective: To investigate the role of the substantia nigra pars reticulata (SNr) in saccadic mask-induced inhibition in Parkinson’s disease.

Background: Saccadic mask-induced inhibition (SMII) delays saccadic initiation following the presentation of a visual distractor immediately after a saccadic target. This inhibition is thought to result from a competition between the target and the distractor visuomotor plans that might involve the superior colliculus (Reingold and Stampe, 2002, 2004). Here, we tested if the substantia nigra pars reticulata (SNr) plays a role in SMII as it sends exogenous inhibitory input to SC through strong GABAergic connections (Behan et al., 1987, Bickford and Hall, 1992). Oculomotor behavior is affected by Parkison’s disease (PD). PD is characterized by a loss of dopaminergic neurons within the Substantia Nigra leading to several motor impairments (Damier et al., 1999).

Method: The eye movements were recorded in 8 PD patients and 6 healthy controls while performing an SMII task. Briefly, after a short fixation period, the target appears randomly leftward or rightward. In 25% of trials, a structured mask (additional dots) covered the target shortly (90 ms) after the target onset. For each trial, the latency of the saccade was extracted.

Results: The preliminary results show that SMII affects differently the patients than the controls. The effect of the mask affects the controls’ latency distribution up to (214 +- 0.04) ms. The mask effect on the patients’ latency distribution reaches (0.341 +- 0.037) ms. This difference is statistically significant (t-test = -5.653, df = 10, p-value < 0.001).

Conclusion: These preliminary results suggest that oculomotor function is abnormal in PD indicates that the basal ganglia plays a role in the saccadic mask-induced inhibition.

References: [Behan et al., 1987] Behan, M., C-S. Lin, and W. C. Hall. “The nigrotectal projection in the cat: an electron microscope autoradiographic study.” Neuroscience 21.2 (1987): 529-539.
[Bickford and Hall, 1992] Bickford, M. E., and W. C. Hall. “The nigral projection to predorsal bundle cells in the superior colliculus of the rat.” Journal of Comparative Neurology 319.1 (1992): 11-33.
[Damier et al., 1999] P Damier, EC Hirsch, Y Agid, AM Graybiel The substantia nigra of the human brain. II. Patterns of loss of dopamine-containing neurons in Parkinson’s disease Brain. 1999 Aug:122 ( Pt 8):1437-48.
[Reingold and Stampe, 2002] Reingold, Eyal M., and Dave M. Stampe. “Saccadic inhibition in voluntary and reflexive saccades.” Journal of cognitive neuroscience 14.3 (2002): 371-388.
[Reingold and Stampe, 2004] Reingold, Eyal M., and Dave M. Stampe. “Saccadic inhibition in reading.” Journal of Experimental Psychology: Human perception and performance 30.1 (2004): 194.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/saccadic-mask-induced-inhibition-in-parkinsons-disease/