Double saccadic pulses and macrosaccadic oscillations from a focal brainstem lesion

Area of Science:

• Neuroscience
• Ophthalmology
• Neurology

Background:

• Double saccadic pulses (DSP) are saccadic intrusions characterized by an initial outward saccade followed by a rapid return saccade to the point of fixation.
• Previous reports of DSP have primarily been associated with diffuse neurological conditions such as multiple sclerosis and metabolic encephalopathy.
• DSP have not previously been described in the context of a circumscribed brain lesion.

Observation:

• This study reports a unique case of a patient experiencing nearly continuous DSP.
• The patient also exhibited macrosaccadic oscillations interspersed between the DSP.
• These oculomotor abnormalities originated from a circumscribed lesion in the dorsal pontine tegmentum, extending to the midbrain.

Findings:

• The lesion affected the dorsal pontine tegmentum but spared the nucleus raphe interpositus, which houses the omnipause neurons crucial for saccade control.
• The observed DSP and macrosaccadic oscillations suggest a potential disruption of the projections from the superior colliculus to these omnipause neurons.
• This localized brainstem lesion provides a novel model for understanding the pathophysiology of saccadic intrusions and oscillations.

Implications:

• The findings suggest that damage to specific brainstem pathways, particularly those involving superior colliculus projections to omnipause neurons, can cause significant saccadic abnormalities.
• This case expands the known clinical spectrum associated with DSP and highlights the importance of localized lesions in oculomotor dysfunction.
• Understanding this mechanism may aid in diagnosing and potentially treating saccadic intrusions and oscillations in patients with focal brainstem lesions.