The nervous system has evolved to gather information about an organisms immediate external and internal environment, assess it on a moment-by-moment basis and make decisions about the motor actions which are most likely to help the organism survive and reproduce. The cerebral cortex is where it all comes together: where incoming sensory information is processed, where decisions about appropriate motor action are made and where said actions are planned and controlled. To achieve all this, the cerebral cortex has specialized into multiple sensory, motor and associational areas, each consisting of myriads of synaptic circuits, but all constructed out of the same basic building blocks … excitatory and inhibitory neurons. Only one in five cortical neurons is inhibitory, typically functioning as a local interneuron. Far from being homogenous, inhibitory interneurons are a diverse assembly of multiple subtypes that differ in their morphology, chemistry and physiology, as well as in the positions they occupy in cortical microcircuits. Two well-studied subtypes of inhibitory interneurons are those expressing the calcium binding protein parvalbumin (PV), and those containing the neuropeptide somatostatin (SOM). PV cells tend to synapse mainly on the perisomatic region of their target neurons, receive initially strong but depressing inputs from upstream excitatory cells, and influence one another via both electrical synapses (gap junctions) and chemical inhibitory synapses. In contrast, SOM cells, with their dendritic-targeting axons, strongly facilitating excitatory input, and within-group electrical, but not chemical, synapses, clearly are poised to play a different role in a given neuronal network. Adding to the complexity are inhibitory connections between different classes of interneurons … for example, a third major class of inhibitory interneurons, those expressing the serotonin 3A receptor, seem to specialize in inhibiting interneurons of other classes.
Why does the cortex need such a diversity of inhibitory cell types? After all, inhibition is inhibition is inhibition; or is it? Are there multiple flavorsŽ of inhibition, each mediated by a different subtype? How do the different subtypes contribute to the operation of the cortical circuits they comprise, to the functioning of the cortical regions these circuits are embedded in, and ultimately to the behavior of the animal or human? These and similar questions will be tackled and discussed in this Frontiers Research Topic collection of articles. Topics that would fit under our rather broad title would be, for example, roles played by different inhibitory subtypes in sensory computations (e.g. divisiveŽ vs. subtractiveŽ roles); roles played by different subtypes during cognitive or motor tasks; roles played by different subtypes when an animal is alert, drowsy or asleep; and how cellular or circuit-level impairments in specific inhibitory subtypes contribute to neurological and mental disorders such as epilepsy, autism and schizophrenia. Beyond being simply a collection of research papers on inhibitory interneurons, this Frontiers Research Topic is intended to serve as a forum for cellular, circuit, systems and computational investigators to "compare notes", debate their different points of view and agree or disagree about various aspects of this exciting and rapidly evolving area of neuroscience research.
The nervous system has evolved to gather information about an organisms immediate external and internal environment, assess it on a moment-by-moment basis and make decisions about the motor actions which are most likely to help the organism survive and reproduce. The cerebral cortex is where it all comes together: where incoming sensory information is processed, where decisions about appropriate motor action are made and where said actions are planned and controlled. To achieve all this, the cerebral cortex has specialized into multiple sensory, motor and associational areas, each consisting of myriads of synaptic circuits, but all constructed out of the same basic building blocks … excitatory and inhibitory neurons. Only one in five cortical neurons is inhibitory, typically functioning as a local interneuron. Far from being homogenous, inhibitory interneurons are a diverse assembly of multiple subtypes that differ in their morphology, chemistry and physiology, as well as in the positions they occupy in cortical microcircuits. Two well-studied subtypes of inhibitory interneurons are those expressing the calcium binding protein parvalbumin (PV), and those containing the neuropeptide somatostatin (SOM). PV cells tend to synapse mainly on the perisomatic region of their target neurons, receive initially strong but depressing inputs from upstream excitatory cells, and influence one another via both electrical synapses (gap junctions) and chemical inhibitory synapses. In contrast, SOM cells, with their dendritic-targeting axons, strongly facilitating excitatory input, and within-group electrical, but not chemical, synapses, clearly are poised to play a different role in a given neuronal network. Adding to the complexity are inhibitory connections between different classes of interneurons … for example, a third major class of inhibitory interneurons, those expressing the serotonin 3A receptor, seem to specialize in inhibiting interneurons of other classes.
Why does the cortex need such a diversity of inhibitory cell types? After all, inhibition is inhibition is inhibition; or is it? Are there multiple flavorsŽ of inhibition, each mediated by a different subtype? How do the different subtypes contribute to the operation of the cortical circuits they comprise, to the functioning of the cortical regions these circuits are embedded in, and ultimately to the behavior of the animal or human? These and similar questions will be tackled and discussed in this Frontiers Research Topic collection of articles. Topics that would fit under our rather broad title would be, for example, roles played by different inhibitory subtypes in sensory computations (e.g. divisiveŽ vs. subtractiveŽ roles); roles played by different subtypes during cognitive or motor tasks; roles played by different subtypes when an animal is alert, drowsy or asleep; and how cellular or circuit-level impairments in specific inhibitory subtypes contribute to neurological and mental disorders such as epilepsy, autism and schizophrenia. Beyond being simply a collection of research papers on inhibitory interneurons, this Frontiers Research Topic is intended to serve as a forum for cellular, circuit, systems and computational investigators to "compare notes", debate their different points of view and agree or disagree about various aspects of this exciting and rapidly evolving area of neuroscience research.
