ABSTRACT
The posteromedial thalamus (POm) has extensive recurrent connectivity with the whisker-related primary somatosensory cortex (wS1) of rodents. However, its functional contribution to somatosensory processing in wS1 remains unclear. This article reviews several recent findings, which begin to elucidate the role of POm in sensory-evoked plasticity and discusses their implications for somatosensory processing.
Subject(s)
Evoked Potentials, Somatosensory , Neuronal Plasticity , Thalamus/physiology , Animals , Humans , Somatosensory Cortex/physiologySubject(s)
Visual Cortex , Animals , Brain-Derived Neurotrophic Factor , Down-Regulation , Rats , Receptor, trkB , SynapsesSubject(s)
Vibrissae , Wakefulness , Animals , Brain , Cerebral Cortex , Mice , Somatosensory CortexABSTRACT
The sensory cortex receives synaptic inputs from both first-order and higher-order thalamic nuclei. First-order inputs relay simple stimulus properties from the periphery, whereas higher-order inputs relay more complex response properties, provide contextual feedback, and modulate plasticity. Here, we reveal that a cortical neuron's higher-order input is determined by the type of progenitor from which it is derived during embryonic development. Within layer 4 (L4) of the mouse primary somatosensory cortex, neurons derived from intermediate progenitors receive stronger higher-order thalamic input and exhibit greater higher-order sensory responses. These effects result from differences in dendritic morphology and levels of the transcription factor Lhx2, which are specified by the L4 neuron's progenitor type. When this mechanism is disrupted, cortical circuits exhibit altered higher-order responses and sensory-evoked plasticity. Therefore, by following distinct trajectories, progenitor types generate diversity in thalamocortical circuitry and may provide a general mechanism for differentially routing information through the cortex.
Subject(s)
Somatosensory Cortex , Thalamus , Transcription Factors , Animals , Mice , Thalamus/cytology , Thalamus/embryology , Thalamus/physiology , Transcription Factors/metabolism , Somatosensory Cortex/cytology , Somatosensory Cortex/physiology , LIM-Homeodomain Proteins/metabolism , LIM-Homeodomain Proteins/genetics , Neurons/cytology , Neurons/physiology , Neurons/metabolism , Neuronal Plasticity/physiology , Mice, Inbred C57BLABSTRACT
The mammalian neocortex is characterized by a variety of neuronal cell types and precise arrangements of synaptic connections, but the processes that generate this diversity are poorly understood. Here we examine how a pool of embryonic progenitor cells consisting of apical intermediate progenitors (aIPs) contribute to diversity within the upper layers of mouse cortex. In utero labeling combined with single-cell RNA-sequencing reveals that aIPs can generate transcriptionally defined glutamatergic cell types, when compared to neighboring neurons born from other embryonic progenitor pools. Whilst sharing layer-associated morphological and functional properties, simultaneous patch clamp recordings and optogenetic studies reveal that aIP-derived neurons exhibit systematic biases in both their intralaminar monosynaptic connectivity and the post-synaptic partners that they target within deeper layers of cortex. Multiple cortical progenitor pools therefore represent an important factor in establishing diversity amongst local and long-range fine-scale glutamatergic connectivity, which generates subnetworks for routing excitatory synaptic information.