Pure topographic disorientation due to right retrosplenial lesion

TLDR

Correlated spiking activity dominates immature cortical networks and is thought to aid circuit maturation, but its spatiotemporal organization remains unclear. Wide‑field calcium imaging of neonatal rat brain slices revealed traveling waves that begin in the anterior lateral entorhinal cortex and propagate across cortex, with layer III neurons activated first at wave onset. The waves depend on glutamatergic transmission, involve balanced glutamate and GABA inputs, and are driven by layer III neurons that are autonomously active, lead the wave front, and maintain activity during reflections, underscoring layer III’s role in early cortical network maturation.

Abstract

Correlated spiking activity prevails in immature cortical networks and is believed to contribute to neuronal circuit maturation; however, its spatiotemporal organization is not fully understood. Using wide-field calcium imaging from acute whole-brain slices of rat pups on postnatal days 1–6, we found that correlated spikes were initiated in the anterior part of the lateral entorhinal cortex and propagated anteriorly to the frontal cortex and posteriorly to the medial entorhinal cortex, forming traveling waves that engaged almost the entire cortex. The waves were blocked by ionotropic glutamatergic receptor antagonists but not by GABAergic receptor antagonists. During wave events, glutamatergic and GABAergic synaptic inputs were balanced and induced UP state-like depolarization. Magnified monitoring with cellular resolution revealed that the layer III neurons were first activated when the waves were initiated. Consistent with this finding, layer III contained a larger number of neurons that were autonomously active, even under a blockade of synaptic transmission. During wave propagation, the layer III neurons constituted a leading front of the wave. The waves did not enter the parasubiculum; however, in some cases, they were reflected at the parasubicular border and propagated back in the opposite direction. During this reflection process, the layer III neurons in the medial entorhinal cortex maintained persistent activity. Thus, our data emphasize the role of layer III in early network behaviors and provide insight into the circuit mechanisms through which cerebral cortical networks maturate.