Abstracts

Rationale: Ictal discharges originating from a brain region propagate along specific neuroanatomical pathways and recruit specific neural structures that are interconnected with the ictal onset zone. In order to understand the routes of propagation of medial temporal lobe seizures, and the neuroanatomical correlates of ictal behavior in temporal lobe epilepsy, it is essential to have a complete map of the anatomical connections of the medial temporal lobe structures with cortical as well as subcortical structures. While there is a wealth of knowledge about the hippocampal, parahippocampal and amygdalar connections, there is only scarce evidence in primates about the connectivity of the temporal polar region. As it is relevant for the studies of the neural correlates of ictal behavior, we report here the connectivity of temporal pole and its adjacent cortices with cortical and subcortical structures involved in behavioral outputs. Methods: Serial brain sections were obtained in six cynomolgus monkeys (Macaca Fasicularis) injected in various locations of the temporal pole and the areas immediately posterior to the polar region with anterograde tracers of Biotinylated dextranamine (BDA) and FlouroRuby (FR). Serial microscopical sections of the brain that had been processed for the visualization of the tracers were reviewed using Neurolucida System (Microbright®). Synaptic terminals and axonal projections were charted under a microscope interfaced with a motorized stage and computer. Connectivity maps were created for the entire brain including all cortical and subcortical structures. Results: Our findings indicate that the medial and lateral temporal pole (Brodman area, BA 38) have strong projections to the orbitofrontal and ventromedial prefrontal cortex, agranular insula, BA32, BA24a/b, and the motor region of the anterior cingulate cortex (BA 24c). Injections further posterior and outside BA38 (in the superior or inferior temporal gyri) revealed no projections to these regions. Moreover, within the brainstem, the temporal polar projections targeted the periaqueductal gray matter (PAG) and the parabrachial nucleus (PBN). Projections from the posterior superior temporal gyrus projected to the core of the inferior colliculus and nucleus of lateral lemniscus in addition to the superior colliculus and the pontine nuclei of the basis pontis. Projections to the inferior temporal cortex spared the brainstem. Conclusions: Epileptic discharges originating from the temporal polar region can target agranular limbic cortices of the orbitofrontal, anterior cingulate, and insular cortices as well as brainstem structures such as the PAG.