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Memory guided saccades in mesial temporal lobe epilepsy with hippocampal sclerosis
S Colnaghi1, C Arbasino, G Beltrami
1Laboratorio Movimenti Oculari, Fondazione Istituto Neurologico C. Mondino IRCCS, Dipartimento di Scienze Neurologiche, Università degli Studi di Pavia, Italy. si.co@libero.it
Objective:
Mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) may involve extrahippocampal areas of structural and functional damage. The incidence and the features of this damage are still a matter of debate and vary depending on the method applied. Memory guided saccades (MGSs) with a memorization delay longer than 20s can be used reliably to evaluate the parahippocampal cortex.
Methods:
MGSs with 3 and 30s memorization delays were recorded with the search coil technique in six patients affected by right MTLE-HS, and in 13 healthy controls.
Results:
The patients were not able to reduce the MGSs residual amplitude error after the first saccade with a 30s memorization delay. This finding was more evident with leftward saccades.
Conclusions:
MGS abnormalities suggested the functional involvement of the right parahippocampal cortex in most of the patients with MTLE-HS, and this supports the clinical and anatomopathological heterogeneity of the disease.
Significance:
MGSs can be used in patients with right MTLE-HS to detect a possible functional involvement of the ipsilateral parahippocampal cortex.
Insights
Memory guided saccades (MGSs) reveal functional parahippocampal cortex involvement in mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS). This suggests MTLE-HS may affect brain areas beyond the hippocampus.
Area of Science:
- Neuroscience
- Epileptology
- Clinical Neurology
Background:
- Mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) may extend beyond hippocampal damage.
- The extent and characteristics of extrahippocampal damage in MTLE-HS remain debated.
- Memory guided saccades (MGSs) offer a method to assess parahippocampal cortex function, especially with longer delays.
Purpose of the Study:
- To investigate potential functional involvement of extrahippocampal areas, specifically the parahippocampal cortex, in patients with right MTLE-HS.
- To evaluate the utility of memory guided saccades (MGSs) with extended memorization delays in detecting parahippocampal dysfunction.
Main Methods:
- Memory guided saccades (MGSs) were recorded using the search coil technique.
- Participants included six patients with right MTLE-HS and 13 healthy controls.
- MGSs were assessed with 3-second and 30-second memorization delays.
Main Results:
- Patients with MTLE-HS demonstrated an inability to reduce MGS residual amplitude error after the first saccade at a 30s delay.
- This deficit in MGS performance was more pronounced with leftward saccades.
- Abnormalities in MGS performance suggest impaired function.
Conclusions:
- MGS abnormalities indicate functional involvement of the right parahippocampal cortex in a majority of MTLE-HS patients.
- These findings support the concept of clinical and anatomopathological heterogeneity in MTLE-HS.
- MGSs are a viable tool for detecting potential ipsilateral parahippocampal cortex involvement in right MTLE-HS.
