Cortical control of voluntary saccades in Parkinson's disease and pre-emptive perception.

Gamma range EEG has been associated with cognition. Bodis-Wollner et al. [Ann NY Acad Sci 2002;956:464-7] and Forgacs et al. [Perception 2008;37:419-32] described posterior perisaccadic gamma (35-45 Hz) modulation associated with voluntary saccades. Voluntary impairment is a hallmark of Parkinson's disease (PD). We have done correlational analysis of frontally and posteriorly (posterior-parietal) recorded intrasaccadic gamma (ISG) powers, to understand cortical control of voluntary saccades in PD and healthy controls. Fifteen PD patients (55-71 years, 4 females) and 17 healthy controls (54-72 years, 9 females) participated in the study. The EEG was recorded over frontal and posterior-parietal scalp sites. Saccades were recorded with electro-oculogram and infra-red ISCAN camera. Subjects executed horizontal voluntary saccades to a mark; 15 degree distance rightwards or leftwards (centrifugal CF) from the central fixation, then back to the center (centripetal CP) and so on, for 2 minutes. Perisaccadic EEG segments were wavelet transformed followed by Hilbert transform to obtain ISG (35-45 Hz) powers. ISG power was trial-averaged, separately for the 4 possible saccade types; CP and CF, rightwards and leftwards. The perisaccadic EEG revealed disorganization in the intrasaccadic period. The correlations between frontal and posterior ISG power are high in PD (correlation coefficient >0.6) while low in controls (correlation coefficient <0.02). We interpret these results as lack of modulatory coupling between frontal and posterior intrasaccadic mechanisms in PD. Impaired volition in PD may be due to impaired circuitry of preemptive perception (PEP). Interareal phase coupling analysis will help in investigating the cortical voluntary saccade control with greater temporal precision.

Perisaccadic gamma modulation in Parkinson disease patients and healthy subjects.

We quantified the anterior-posterior distribution of the gamma modulation index (GMI), an index of perisaccadic phasic modulation of the gamma (35-45 Hz) range electroencephalogram (EEG), in healthy human subjects and Parkinson disease (PD) patients. The EEG was recorded over the frontal, parietal, temporal and occipital sites in 11 idiopathic PD patients (age 50-70 years, four females), 4 age matched healthy volunteers (1 female) and 17 young healthy controls (age 21-30 years, four females) Eye movements were recorded with EOG and ISCAN camera. Subjects executed saccades to a mark at right and back to fixation point and vice versa. The saccades directed away from center/fixation (centrifugal CF) were analyzed. Two minutes of EEG were obtained from each subject for the two possible saccade types (centrifugal rightwards and leftwards at 15 degrees). Each perisaccadic EEG segment was analyzed using continuous wavelet transform for quantifying the power and time course of gamma EEG ranges for each saccade type. A three way ANOVA was used for statistical analysis. Perisaccadic GMI (peak intrasaccadic power divided by mean power) in healthy subjects was higher over the contralateral hemisphere to the saccade direction, for both centrifugal saccades at anterior, posterior and occipital recording sites. Contrary to the healthy subject GMI remained near one in PD, i.e., there was no evidence of intrasaccadic gamma power increase in PD patients.

Aneurysm surgery in Pakistan.

The purpose of this study was to find out the incidence and outcome of aneurysms being operated in Pakistan. The data was collected from various neurosurgical centers in Pakistan where facilities for aneurysm surgery are available. The population of Pakistan is 130 million, with 28 neurosurgical centers in the country but only eight are equipped with facilities for performing aneurysm surgery. The period of study extended from January 1994 to December 1996. During this period 350 patients presented with subarachnoid hemorrhage (SAH). Diagnosis of SAH was confirmed by computed tomography (CT) brain scan, diagnostic lumbar puncture was performed in few patients only where CT scan was negative. After angiography, 240 patients had intracranial aneurysms, 79 had arteriovenous malformations, and three had bled in brain tumors. Of the 240 patients with proven intracranial aneurysms, 122 (51%) were male and 118 (49%) were female. The mean age at presentation was 40.5 years with a range from 7 to 68 and a peak incidence between 41 and 50 years. Subarachnoid bleeding was noticed in 179 (74.6%) patients, 52 (21.7%) had SAH associated with intracerebral hemorrhage, and nine (4%) patients presented with the third cranial nerve palsy. Anterior communicating artery was the commonest site for aneurysms (120, 50%), followed by posterior communicating artery (46, 19%) and middle cerebral artery (45, 19%). Aneurysm surgery was performed in 134 (56%) patients. Operative mortality was about 10%. At 3 months follow up 49% patients were in grade I Glasgow Outcome Scale. We conclude that intracranial aneurysms occur with equal frequency in both sexes with a peak incidence between 41-50 years and anterior communicating artery is the commonest site. SAH is the most common mode of presentation and is still a neglected from of stroke in Pakistan. Medical specialists and family physicians require education for early diagnosis and timely referral of patients with SAH to neurosurgical centers.