Causal oscillations in the visual thalamo-cortical network in sustained attention in ferrets

Sustained visual attention allows us to process and react to unpredictable, behaviorally relevant sensory input. Sustained attention engages communication between the higher-order visual thalamus and its connected cortical regions. However, it remains unclear whether there is a causal relationship between oscillatory circuit dynamics and attentional behavior in these thalamo-cortical circuits. By using rhythmic optogenetic stimulation in the ferret, we provide causal evidence that higher-order visual thalamus coordinates thalamo-cortical and cortico-cortical functional connectivity during sustained attention via spike-field phase locking. Increasing theta but not alpha power in the thalamus improved accuracy and reduced omission rates in a sustained attention task. Further, the enhancement of effective connectivity by stimulation was correlated with improved behavioral performance. Our work demonstrates a potential circuit-level causal mechanism for how the higher-order visual thalamus modulates cortical communication through rhythmic synchronization during sustained attention.

Properties of Deiters' neurons and inhibitory synaptic transmission in the mouse lateral vestibular nucleus

Deiters' neurons, located exclusively in the lateral vestibular nucleus (LVN), are involved in vestibulospinal reflexes, innervate extensor motoneurons that drive anti-gravity muscles, and receive inhibitory inputs from the cerebellum. We investigated intrinsic membrane properties, short-term plasticity, and inhibitory synaptic inputs of mouse Deiters' and non-Deiters' neurons within the LVN. Deiters' neurons are distinguished from non-Deiters' neurons by their very low input resistance (105.8 vs 521.8 MOhms) respectively, long axons that project as far as the ipsilateral lumbar spinal cord, and expression of the cytostructural protein, non-phosphorylated neurofilament protein (NPNFP). Whole-cell patch clamp recordings in brainstem slices show most Deiters' and non-Deiters' neurons were tonically active (>92%). Short-term plasticity was studied by examining discharge rate modulation following release from hyperpolarization (post-inhibitory rebound firing; PRF) and depolarization (firing rate adaptation; FRA). PRF and FRA gain were similar in Deiters' and non-Deiters' neurons (PRF: 24.9 vs. 20.2 Hz and FRA gain: 231.5 vs. 287.8 spikes/sec/nA respectively). Inhibitory synaptic input to both populations showed GABAergic rather than glycinergic inhibition dominated in Deiters' neurons and GABA_A miniature inhibitory postsynaptic current (mIPSC) frequency was much higher in Deiters' neurons compared to non-Deiters' neurons (~15.9 vs. 1.4 Hz respectively). Our data suggest Deiters' neurons can be reliably identified by their intrinsic membrane and synaptic properties. They are tonically active, glutamatergic, have low sensitivity or 'gain', exhibit little adaptation, and receive strong GABAergic input. Together, these features suggest, since Deiters' neurons have minimal short-term plasticity they are well-suited to a role encoding tonic signals for the vestibulospinal reflex.

Transcranial alternating current stimulation entrains alpha oscillations by preferential phase synchronization of fast-spiking cortical neurons to stimulation waveform

Computational modeling and human studies suggest that transcranial alternating current stimulation (tACS) modulates alpha oscillations by entrainment. Yet, a direct examination of how tACS interacts with neuronal spiking activity that gives rise to the alpha oscillation in the thalamo-cortical system has been lacking. Here, we demonstrate how tACS entrains endogenous alpha oscillations in head-fixed awake ferrets. We first show that endogenous alpha oscillations in the posterior parietal cortex drive the primary visual cortex and the higher-order visual thalamus. Spike-field coherence is largest for the alpha frequency band, and presumed fast-spiking inhibitory interneurons exhibit strongest coupling to this oscillation. We then apply alpha-tACS that results in a field strength comparable to what is commonly used in humans (<0.5 mV/mm). Both in these ferret experiments and in a computational model of the thalamo-cortical system, tACS entrains alpha oscillations by following the theoretically predicted Arnold tongue. Intriguingly, the fast-spiking inhibitory interneurons exhibit a stronger entrainment response to tACS in both the ferret experiments and the computational model, likely due to their stronger endogenous coupling to the alpha oscillation. Our findings demonstrate the in vivo mechanism of action for the modulation of the alpha oscillation by tACS.

Stimulus-specific regulation of visual oddball differentiation in posterior parietal cortex

The frequency at which a stimulus is presented determines how it is interpreted. For example, a repeated image may be of less interest than an image that violates the prior sequence. This process involves integration of sensory information and internal representations of stimulus history, functions carried out in higher-order sensory areas such as the posterior parietal cortex (PPC). Thus far, there are few detailed reports investigating the single-neuron mechanisms for processing of stimulus presentation frequency in PPC. To address this gap in knowledge, we recorded PPC activity using 2-photon calcium imaging and electrophysiology during a visual oddball paradigm. Calcium imaging results reveal differentiation at the level of single neurons for frequent versus rare conditions which varied depending on whether the stimulus was preferred or non-preferred by the recorded neural population. Such differentiation of oddball conditions was mediated primarily by stimulus-independent adaptation in the frequent condition.