How sleep influences brain plasticity is not known. In particular, why certain electroencephalographic (EEG) rhythms are linked to memory consolidation is poorly understood. Calcium activity in dendrites is known to be necessary for structural plasticity changes, but this has never been carefully examined during sleep. Here, we report that calcium activity in populations of neocortical dendrites is increased and synchronised during oscillations in the spindle range in naturally sleeping rodents. Remarkably, the same relationship is not found in cell bodies of the same neurons and throughout the cortical column. Spindles during sleep have been suggested to be important for brain development and plasticity. Our results provide evidence for a physiological link of spindles in the cortex specific to dendrites, the main site of synaptic plasticity.

The action potential activity of single cortical neurons can evoke measurable sensory effects, but it is not known how spiking parameters and neuronal subtypes affect the evoked sensations. Here, we examined the effects of spike train irregularity, spike frequency, and spike number on the detectability of single-neuron stimulation in rat somatosensory cortex. For regular-spiking, putative excitatory neurons, detectability increased with spike train irregularity and decreasing spike frequencies but was not affected by spike number. Stimulation of single, fast-spiking, putative inhibitory neurons led to a larger sensory effect compared to regular-spiking neurons, and the effect size depended only on spike irregularity. An ideal-observer analysis suggests that, under our experimental conditions, rats were using integration windows of a few hundred milliseconds or more. Our data imply that the behaving animal is sensitive to single neurons' spikes and even to their temporal patterning.

Declarative memory formation is believed to rely on interactions between the medial temporal lobe (MTL) and neocortex. However, the distributed nature of neocortical networks has hindered investigation on cellular targets and mechanisms of memory formation in the neocortex. The six-layered mammalian neocortex has an anatomical organization in which top-down inputs converge on its outermost layer, layer 1 (L1). We investigated this organization to examine how layer-specific MTL inputs modulate neocortical activity and memory formation. To this end, we first adapted a cortical-and hippocampal-dependent learning paradigm, in which animals were trained to associate direct cortical microstimulation and reward, and characterized learning behavior of rats and mice during this task. We next showed that neurons in the deep layers of the perirhinal cortex not only provide monosynaptic inputs to L1 of the primary somatosensory cortex (S1), where microstimulation was presented, but also actively reflect the behavioral outcome. Chemogenetic suppression of perirhinal inputs to L1 of S1 disrupted early memory formation but did not affect animals' performance after learning. The learning was followed by an emergence of a distinct subpopulation of layer 5 (L5) pyramidal neurons (~10%) characterized by high-frequency burst firing, which could be reduced by blocking perirhinal inputs to L1. Interestingly, similar proportion of apical dendrites (~10%) of L5 pyramidal neurons also displayed significantly enhanced calcium (Ca 2+ ) activity during memory retrieval in expert animals. Importantly, disrupting dendritic Ca 2+ activity impaired learning, suggesting that apical dendrites of L5 pyramidal neurons have a critical role in neocortical memory formation. Taken together, these results suggest that MTL inputs control learning via a perirhinal-mediated gating process in L1, manifested by elevated dendritic Ca 2+ activity and burst firing in L5 pyramidal neurons. The present study provides insights into cellular mechanisms of learning and memory representations in the neocortex. Zusammenfassung SHIN (2020) ___________________________________________________________________________ 2 Zusammenfassung Es wird angenommen, dass deklarative Gedächtnisbildung auf Wechselwirkungen zwischen dem medialen Temporallappens (MTL) und dem Neokortex beruht. Die Untersuchung der zellulären Ziele und Mechanismen von Gedächtnisbildung im Neokortex wird erschwert durch die über den Kortex verteilte Struktur neokortikaler Netzwerke. Der in sechs Schichten gegliederte Neokortex von Säugetieren besitzt eine anatomische Organisation, in der Top-Down-Inputs inseiner äußersten Schicht, Schicht 1 (L1), konvergieren. Wir haben diese Organisation untersucht, um zu verstehen, wie schichtspezifische MTL-Inputs die neokortikale Aktivität und die Gedächtnisbildung modulieren. Zu diesem Zweck haben wir ein Kortex-und Hippocampus-abhängiges Lernparadigma angepasst, in dem Tiere darauf trainiert wurden, direkte kortikale Mikrostimulation und Belohnung zu assoziieren, und...

Anatomical, stimulation and lesion data implicate vibrissa motor cortex in whisker motor control. Work on motor cortex has focused on movement generation, but correlations between vibrissa motor cortex activity and whisking are weak. The exact role of vibrissa motor cortex remains unknown. We recorded vibrissa motor cortex neurons during various forms of vibrissal touch, which were invariably associated with whisker protraction and movement. Free whisking, object palpation and social touch all resulted in decreased cortical activity. To understand this activity decrease, we performed juxtacellular recordings, nanostimulation and in vivo whole-cell recordings. Social touch resulted in decreased spiking activity, decreased cell excitability and membrane hyperpolarization. Activation of vibrissa motor cortex by intracortical microstimulation elicited whisker retraction, as if to abort vibrissal touch. Various vibrissa motor cortex inactivation protocols resulted in contralateral protraction and increased whisker movements. These data collectively point to movement suppression as a prime function of vibrissa motor cortex activity.