Table 1.

Novel technologies used to characterize the social circuit.

Technique	Description	Example Use
Optogenetics	Light-based activation or inhibition of neuronal populations genetically induced to express light-sensitive ion channels.	Expression of inhibitory opsins in the the projects from CA1 to NAc were used to demonstrate the necessity of this projection for social recognition (Okuyama, 2016).
Chemogenetics	Chemical activation or inhibition of neuronal populations through the expression of genetically modified receptors and administration of an engineered ligand to modulate neuronal activity.	Inhibition of Crus 1 Purkinje cells through the expression of inhibitory DREADD receptors demonstrated the functional connectivity between this region and the parietal cortex (Stoodley, 2017).
Amperometry	Electrochemical technique to detect transient current changes induced by an oxidation reaction associated with the vesicular release of specific neurotransmitters.	Reduced dopamine efflux was detected in the prefrontal cortex via fixed potential amperometry in lurcher mice after electrical stimulation of cerebellar Purkinje outputs (Mittleman, 2008).
Calcium imaging	Fluorescent reporter of dynamic fluctuations in calcium levels related to neuronal activity that can be read via two-photon imaging,, microendoscopes or fiber photometry.	Viral mediated expression of the calcium reporter GCaMP in dopaminergic VTA neurons was used to indicate the release of dopamine in response to social stimuli. Fluorescence was detected using fiber photometry to demonstrate an increase in dopaminergic activity during social interaction (Gunaydin, 2014).
Multi-electrode recording	Recording of single neuron activity through the implantation of arrays of bundled electrodes that allow the isolation of individual units of activity.	In vivo multielectrode recordings in the VMH of male was used to identify two subsets of neuron populations that distinctly responded to either male conspecifics in aggressive interactions or female conspecifics in affiliative interactions (Anderson, 2012).
Local field potential recording	Recording of an electrophysiological signal derived from the summed electrical activity in a small volume of tissue often organized into rhythmic oscillatory patterns based on the dynamics of cellular firing.	Local field potential was recorded from the mPFC and NAc of prairie voles to demonstrate socially facilitated functional connectivity between these brain regions evident in the coherence in low frequency oscillations during mating (Amadei, 2017)
Electroencephalography (EEG)	Translational readout of neural activity summed across a large volume of tissue detected at the level of the skull or epidural space from which neural oscillations can be extracted and compared to human electrophysiological readouts.	Electrophysiological recording of cortical EEG signal measured from electrodes embedded in the skull demonstrated an enhancement in gamma power oscillatory activity of Shank3b mice that exhibit robust social behavioral deficits (Dhamne, 2017).
Cell-selective gene manipulation	Promoter driven gene manipulation to selectively modify gene expression within a discrete cell population.	Viral mediated expression of Cre dependent tetanus neurotoxin in a CA2 specific Cre genetically modified mouse line was used to inactivate the output of this region to identify a specific phenotype of social recognition (Hitti, 2014).