Anti-epileptogenesis: Electrophysiology, diffusion tensor imaging and behavior in a genetic absence model.

The beneficial effects of chronic and early pharmacological treatment with ethosuximide on epileptogenesis were studied in a genetic absence epilepsy model comorbid for depression. It was also investigated whether there is a critical treatment period and treatment length. Cortical excitability in the form of electrical evoked potentials, but also to cortico-thalamo-cortical network activity (spike-wave discharges, SWD and afterdischarges), white matter changes representing extra cortico-thalamic functions and depressive-like behavior were investigated. WAG/Rij rats received either ethosuximide for 2 months (post natal months 2-3 or 4-5), or ethosuximide for 4 months (2-5) in their drinking water, while control rats drank plain water. EEG measurements were made during treatment, and 6 days and 2 months post treatment. Behavioral test were also done 6 days post treatment. DTI was performed ex vivo post treatment. SWD were suppressed during treatment, and 6 days and 2 months post treatment in the 4 month treated group, as well as the duration of AD elicited by cortical electrical stimulation 6 days post treatment. Increased fractional anisotropy in corpus callosum and internal capsula on DTI was found, an increased P8 evoked potential amplitude and a decreased immobility in the forced swim test. Shorter treatments with ETX had no large effects on any parameter. Chronic ETX has widespread effects not only within but also outside the circuitry in which SWD are initiated and generated, including preventing epileptogenesis and reducing depressive-like symptoms. The treatment of patients before symptom onset might prevent many of the adverse consequences of chronic epilepsy.

Absence of spatial updating when the visuomotor system is unsure about stimulus motion.

How does the visuomotor system decide whether a target is moving or stationary in space or whether it moves relative to the eyes or head? A visual flash during a rapid eye-head gaze shift produces a brief visual streak on the retina that could provide information about target motion, when appropriately combined with eye and head self-motion signals. Indeed, double-step experiments have demonstrated that the visuomotor system incorporates actively generated intervening gaze shifts in the final localization response. Also saccades to brief head-fixed flashes during passive whole-body rotation compensate for vestibular-induced ocular nystagmus. However, both the amount of retinal motion to invoke spatial updating and the default strategy in the absence of detectable retinal motion remain unclear. To study these questions, we determined the contribution of retinal motion and the vestibular canals to spatial updating of visual flashes during passive whole-body rotation. Head- and body-restrained humans made saccades toward very brief (0.5 and 4 ms) and long (100 ms) visual flashes during sinusoidal rotation around the vertical body axis in total darkness. Stimuli were either attached to the chair (head-fixed) or stationary in space and were always well localizable. Surprisingly, spatial updating only occurred when retinal stimulus motion provided sufficient information: long-duration stimuli were always appropriately localized, thus adequately compensating for vestibular nystagmus and the passive head movement during the saccade reaction time. For the shortest stimuli, however, the target was kept in retinocentric coordinates, thus ignoring intervening nystagmus and passive head displacement, regardless of whether the target was moving with the head or not.

Early and late stages of working-memory maintenance contribute differentially to long-term memory formation.

The present paper investigated the role of early and late stages of working-memory maintenance, which have been suggested to differentially contribute to long-term memory formation. In experiment 1, we administered a delayed-match-to-sample task, requiring participants to remember line drawings of non-sense three-dimensional stimuli. In the delay phase, participants were either presented with a fixation cross (for 2 or 9s) or with one of two different interference tasks, varying in visual overlap with the target. The interference task was presented 1.5, 4.5 or 7.5s after target offset. Early interfering and early probing disproportionately affected performance on an unexpected subsequent recognition-memory task compared to later interference or probing. This was not modulated by the type of interference task. In Experiment 2, we examined whether the formation of a holistic internal code of the target may be a gradual process. An analogous delayed-match-to-sample task was administered, with interference after 0.5, 2.5 or 4.5s after target offset. The early and middle interference condition similarly disproportionately affected performance compared to later interference. Hence, the present results support the view of a functional dissociation between early and late stages of working-memory maintenance and that early working-memory processes contribute particularly to long-term memory formation.