Multiunitary activity naalysis of cortical and subcortical structures in paroxysmal discharges and grand mal seizures in photosensitve baboons

Complex partial seizures provoked by photic stimulation

“…Similar constellations were previously reported in individual patients with photoconvulsive reaction who had partial epilepsy and occipital epileptic focus 3. Cortical and subcortical recordings in monkeys during IPS showed paroxysmal discharges predominantly in prerolandic areas, which were followed by bursts in the pontine and mesencephalic reticular formation and, finally, by generalised discharges 4. These findings have been interpreted in favour of a cortical origin of the photoconvulsive reaction, which is supported by the studies of Ricci et al 5 using neuromagnetic methods in humans with photoconvulsive reaction to identify the location of the photoconvulsive reaction generator: They found a regional sensitivity involving frontal, occipital, and temporal areas, but the cortical excitability was extremely unstable, which was attributed to a deficient GABA-ergic system.…”

Does the region of epileptogenicity influence the pattern of change in cortical excitability?

“…Another explanation is that the more extensive inter-hemispheric synaptic connections between extra-temporal lobe regions facilitate the spread or propagation of epileptic activity between these hemispheres when the focus is in these regions. This is supported by evidence from EEG-fMRI studies (Yu et al, 2009;Kobayashi et al, 2006) (Tyvaert et al, 2008) as well as human and animal data (Keller and Roberts, 2008;Blumenfeld et al, 2007); (Holmes et al, 1999;Zilles et al, 1998;Silva-Barrat et al, 1986) which show regional as well as distant cortical and subcortical changes associated with focal interictal spikes, being more so in patients with extra-temporal foci. It also would correlate well with the described increased incidence of bilateral features in extra-temporal lobe seizure semiologies (Luders et al, 1998;Gastaut, 1970) and of bilateral interictal and ictal discharges seen in patients with extra-TLE (Bautista et al, 1998;Taylor et al, 2003;Gibbs and Gibbs, 1955) as opposed to TLE where most reports show that even if bilateral interictal discharges are recorded, they are predominant over the side with seizure onset in 60-70% of patients (Hirsch et al, 1991;Williamson et al, 1993).…”

Modeling the effective connectivity of the visual network in healthy and photosensitive, epileptic baboons

“…These regions were not included in our model because they did not demonstrate significant CBF changes during the PPR in earlier conditional contrast and covariance studies (Szabó et al 2007; Szabó et al 2011). The thalamus is another structure extensively connected with the frontoparietal cortices, which is typically activated in the setting of prolonged generalized spike-and-wave discharges or absence seizures in humans (Bai et al 2010; Benuzzi et al 2012), and in the setting of sustained repetitive IEDs in the epileptic baboon (Fischer-Williams et al 1968; Szabó et al 2008; Silva-Barrat et al 1986). However, as most of the PPRs were brief and PCRs were restricted to brief myoclonic seizures in the PS baboons, it not surprising that the thalamus was not involved or significantly activated.…”