More and more patients worldwide are diagnosed with dementia, which emphasizes the urgent need for early detection markers. In this study, we built on the auditory hypersensitivity theory of a previous study—which postulated that responses to auditory input in the subcortex as well as cortex are enhanced in cognitive decline—, and examined auditory encoding of natural continuous speech at both neural levels for its indicative potential for cognitive decline. We recruited study participants aged 60 years and older, who were divided into two groups based on the Montreal Cognitive Assessment, one group with low scores (n = 19, participants with signs of cognitive decline), and a control group (n = 25). Participants completed an audiometric assessment and then we recorded their electroencephalography while they listened to an audiobook and click sounds. We derived Temporal Response Functions and evoked potentials from the data and examined response amplitudes for their potential to predict cognitive decline, c...

The primary motor cortex (M1) integrates sensory and cognitive inputs to generate voluntary movement. Its functional impairments have been implicated in the pathophysiology of motor symptoms in Parkinson's disease (PD). Specifically, dopaminergic degeneration and basal ganglia dysfunction entrain M1 neurons into the abnormally synchronized bursting pattern of activity throughout the cortico-basal ganglia-thalamocortical network. However, how degeneration of the midbrain dopaminergic neurons affects the anatomy, microcircuit connectivity, and function of the M1 network remains poorly understood. The present study examined whether and how loss of dopamine (DA) affects the morphology, cellular excitability, and synaptic physiology of layer 5 parvalbumin-expressing (PV+) cells in the M1 of mice of both sexes. Here we reported that loss of midbrain dopaminergic neurons does not alter the number, morphology, and physiology of layer 5 PV+ cells in M1. Moreover, we demonstrated that the number of perisomatic PV+ p...

High-density linear probes, like Neuropixels, provide an unprecedented opportunity to understand how neural populations within specific laminar compartments contribute to behavior. Marmoset monkeys, unlike macaque monkeys, have a lissencephalic (smooth) cortex that enables recording perpendicular to the cortical surface, thus making them an ideal animal model for studying laminar computations. Here we present a method for acute Neuropixels recordings in the common marmoset ( Callithrix jacchus ). The approach replaces the native dura with an artificial silicon-based dura that grants visual access to the cortical surface, which is helpful in avoiding blood vessels, ensures perpendicular penetrations, and could be used in conjunction with optical imaging or optogenetic techniques. The chamber housing the artificial dura is simple to maintain with minimal risk of infection and could be combined with semi-chronic microdrives and wireless recording hardware. This technique enables repeated acute penetrations ov...

Forebrain neurons deprived of activity become hyperactive when activity is restored. Rebound activity has been linked to spontaneous seizures in vivo following prolonged activity blockade. Here we measured the time course of rebound activity and the contributing circuit mechanisms using calcium imaging, synaptic staining, and whole cell patch clamp in organotypic slice cultures of mouse neocortex. Calcium imaging revealed hypersynchronous activity increasing in intensity with longer periods of deprivation. While activity partially recovered three days after slices were released from five days of deprivation, they were less able to recover after ten days of deprivation. However, even after the longer period of deprivation, activity patterns eventually returned to baseline levels. The degree of deprivation-induced rebound was age-dependent, with the greatest effects occurring when silencing began in the second week. Pharmacological blockade of NMDA receptors indicated that hypersynchronous rebound activity d...

Both the retina and brain exhibit neurovascular coupling, increased blood flow during increased neural activity. In the retina increased blood flow can be evoked by flickering light, but the magnitude of the metabolic change that underlies this not known. Local changes in oxygen consumption (QO2) are difficult to measure in vivo when both supply and demand are changing. Here we isolated the C57BL/6J mouse retina and supplied it with oxygen from both sides of the tissue. Microelectrode recordings of PO2 were made in darkness and during 20 sec of high scotopic flickering light at 1 Hz. Flicker led to a PO2 increase in the outer retina and a decrease in the inner retina, indicating that outer retinal QO2 (QOR) decreased and inner retinal QO2 (QIR) increased. A four-layer oxygen diffusion model was fitted to PO2 values obtained in darkness and at the end of flicker to determine the values of QOR and QIR. QOR in flicker was 76 ± 14% (mean and SD, n=10) of QOR in darkness. The increase in QIR was smaller, 6.4 ± ...

Sleep spindles appear to play an important role in learning new motor skills. Motor skill learning engages several regions in the brain with two important areas being the motor cortex (M1) and the cerebellum. However, the neurophysiological processes in these areas during sleep, especially how spindle oscillations affect local and cross-region spiking, are not fully understood. We recorded activity from the M1 and cerebellar cortex in 8 rats during spontaneous activity to investigate how sleep spindles in these regions are related to local spiking as well as cross-region spiking. We found that M1 firing was significantly changed during both M1 and cerebellum spindles and this spiking occurred at a preferred phase of the spindle. On average, M1 and cerebellum neurons showed most spiking at the M1 or cerebellum spindle peaks. These neurons also developed a preferential phase-locking to local or cross-area spindles with the greatest phase-locking value at spindle peaks; however, this preferential phase-lockin...

Canonically, action potentials of most mammalian neurons initiate at the axon initial segment and propagate bidirectionally: orthodromically along the distal axon, and retrogradely into the soma and dendrites. Under some circumstances action potentials may initiate ectopically, at sites distal to the axon initial segment, and propagate antidromically along the axon. These ‘ectopic action potentials’ (EAPs) have been observed in experimental models of seizures and chronic pain, and more rarely in nonpathological forebrain neurons. Here we report that a large majority of parvalbumin-expressing (PV+) interneurons in upper layers of mouse neocortex, from both orbitofrontal and primary somatosensory areas, fire EAPs after sufficient activation of their somata. Somatostatin-expressing interneurons also fire EAPs, though less robustly. Ectopic firing in PV+ cells occurs in varying temporal patterns and can persist for several seconds. PV+ cells evoke strong synaptic inhibition in pyramidal neurons and interneuron...

Proprioception, the sense of limb and body position, is required to produce accurate and precise movements. Proprioceptive sensory neurons transmit muscle length and tension information to the spinal cord. The function of excitatory neurons in the intermediate spinal cord, which receive this proprioceptive information, remains poorly understood. Using genetic labeling strategies and patch clamp techniques in acute spinal cord preparations in mice, we set out to uncover how two sets of spinal neurons, Clarke's column (CC) and Atoh1 -lineage neurons, respond to electrical activity and how their inputs are organized. Both sets of neurons are located in close proximity in lamina V-VII of the thoracolumbar spinal cord and have been described to receive proprioceptive signals. We find that a majority of CC neurons have a tonic firing-type and express a distinctive hyperpolarization-activated current (Ih). Atoh1 -lineage neurons, which cluster into two spatially distinct populations, are mostly a fading firing-ty...

Infrared neural stimulation (INS) is a promising area of interest for the clinical application of a neuromodulation method. This is in part because of its low invasiveness, whereby INS modulates the activity of neural tissue mainly through temperature changes. Additionally, INS may provide localized brain stimulation with less tissue damage. The inferior colliculus (IC) is a crucial auditory relay nuclei, and a potential target for clinical application of INS to treat auditory diseases and develop artificial hearing devices. Here, using continuous INS with low to high power density, we demonstrate laminar modulation of neural activity in the mouse IC in the presence and absence of sound. We investigated stimulation parameters of INS to effectively modulate neural activity in a facilitatory or inhibitory manner. A mathematical model of INS-driven brain tissue was first simulated, temperature distributions were numerically estimated, and stimulus parameters were selected from the simulation results. Subseque...

Trace eyeblink conditioning (TEBC) has been widely used to study associative learning in both animals and humans. In this paradigm, conditioned responses (CRs) to conditioned stimuli (CS) serve as a measure for retrieving learned associations between the CS and the unconditioned stimuli (US) within a trial. Memory consolidation i.e. learning over time, can be quantified as an increase in the proportion of CRs across training sessions. However, how hippocampal oscillations differentiate between successful memory retrieval within a session and consolidation across TEBC training sessions remains unknown. To address this question, we recorded local-field potentials (LFPs) from the rat dorsal hippocampus during TEBC and investigated hippocampal oscillation dynamics associated with these two functions. We show that transient broadband responses to the CS were correlated with memory consolidation, as indexed by an increase in CRs across TEBC sessions. In contrast, induced alpha (8–10 Hz) and beta (16–20 Hz) band ...