Topic: two-photon imaging

The Kumar Lab in the Department of Otolaryngology at Washington University in St. Louis runs an NIH-funded program on the cortical cellular and circuit mechanisms behind hearing difficulty in noisy environments after noise-induced hearing loss, integrating systems neuroscience, genetics, pharmacology and computational approaches. Methods include in vivo two-photon imaging of identified neuronal populations in awake mice, auditory behavioral assays, ex vivo brain-slice imaging and electrophysiology, chemogenetic and optogenetic circuit manipulation, inducible conditional knockout mice and pharm

To understand how the brain controls behavior, we need to understand the neural code for movement. Descending neurons (DNs) represent a bottleneck for motor control signals, and so provide an opportunity to study neural coding in a compact form. In Drosophila, almost all DNs are uniquely identifiable in the connectome of the central nervous system and targetable with specific genetic drivers, allowing us to study their connectivity and physiology in parallel. Previous studies have concluded that these DNs generate high-level motor commands, such as “stop” or “turn”, leaving the detailed implem

Layer 5 pyramidal neurons (L5 PNs) are a major cortical output. Their connectivity approximates a recurrent neural network (RNN), with the majority of inputs coming from other L5 PNs. These neurons may underlie anesthesia-induced unconsciousness, by restricting information output from cortex. Therefore, understanding the formation of the L5 PN circuitry, from the time at which L5 PNs first enter cortex, would provide insight into how a biological RNN can be constructed. However, this is technically challenging because, in mice, L5 PNs first enter cortex at embryonic day (E) 13.5, five days bef

Several populations of GABAergic interneurons (INs) are strongly regulated by neuromodulatory input during distinct behavioral states, and thus may be key contributors to flexible cortical function. One prominent model suggests vasoactive intestinal peptide-expressing INs (VIP-INs) activate upon arousal, suppress the activity of downstream INs (SST-INs), and consequently disinhibit pyramidal neurons (PNs). This VIP-SST-PN disinhibitory circuit is hypothesized to be a general cortical circuit motif allowing behavioral state signals to modulate sensory processing. Cortical VIP-INs, however, have

Norepinephrine (NE) is a neuromodulator that is released from projections of the locus coeruleus via extra-synaptic vesicle exocytosis (Fuxe, Borroto-Escuela, front. Physiol 2012). Previously, NE in the prefrontal cortex (PFC) was thought to be a homogenous field created by bulk release, but it remains unknown whether phasic (fast, short-term) fluctuations in NE can produce a spatially heterogeneous field, which could then structure cell firing at a fine spatial scale. To understand how spatiotemporal dynamics of NE release in the PFC affect neuronal firing, we performed a novel in-vivo two-ph

Events occurring close in time are often linked in memory, providing an episodic timeline and a framework for those memories. Recent studies suggest that memories acquired close in time are encoded by overlapping neuronal ensembles, but whether dendritic plasticity plays a role in linking memories is unknown. Using activity-dependent labeling and manipulation, as well as longitudinal one- and two-photon imaging of RSC somatic and dendritic compartments, we show that memory linking is not only dependent on ensemble overlap in the retrosplenial cortex, but also on branch-specific dendritic alloc

Neural computations occurring simultaneously in multiple cerebral cortical regions are critical for mediating behaviors. Progress has been made in understanding how neural activity in specific cortical regions contributes to behavior. However, there is a lack of tools that allow simultaneous monitoring and perturbing neural activity from multiple cortical regions. We have engineered a suite of technologies to enable easy, robust access to much of the dorsal cortex of mice for optical and electrophysiological recordings. First, I will describe microsurgery robots that can programmed to perform

Cholinergic activity is thought to play an important role in learning and the control of brain state. Multiple studies have shown that pairing external phasic stimulation of the cholinergic basal forebrain (CBF) with a sensory stimulus drives long-lasting sensory cortical plasticity, implicating the CBF as a potential substrate for associative learning. For this to be ecologically valid, we hypothesized that CBF projections to the sensory cortex should exhibit phasic signaling that is temporally-synchronous with sensory-evoked responses in cortical neurons. Intrinsic sensory-evoked responses h

The superior colliculus (SC) is a major recipient of visual input in the mouse and controls innate approach and avoidance behaviours. Neurons in the superficial SC (sSC), which receives direct input from the retina, do not only process visual stimuli, but are also modulated by the animal’s running speed and pupil-linked arousal, similar to modulations observed in the primary visual cortex. While these observations were made during passive viewing of visual stimuli, a major purpose of vision is to guide behaviour. We therefore asked whether, in the context of a behavioural task, visual activity

Predicting the sensory consequences of one’s actions is critical to perception and action in dynamically changing environments. For several established sensorimotor behaviours, such as locomotion and vocalizations, neural correlates of this prediction have been reported throughout sensory cortex. Oftentimes, however, the sensory consequences of an action are abstract, context-dependent, and newly learned, such as when one learns to play an instrument. How does cortex represent such complex sensorimotor rules? To investigate this question, we developed a task in which mice manipulated the frequ

Norepinephrine (NE) is a neuromodulator that is released from projections of the locus coeruleus via extra-synaptic vesicle exocytosis. Tonic fluctuations in NE are involved in brain states, such as sleep, arousal, and attention. Previously, NE in the PFC was thought to be a homogenous field created by bulk release, but it remains unknown whether phasic (fast, short-term) fluctuations in NE can produce a spatially heterogeneous field, which could then structure cell firing at a fine spatial scale. To understand how spatiotemporal dynamics of norepinephrine (NE) release in the prefrontal cortex

Hippocampal pyramidal cells have been widely studied during locomotion, when theta oscillations are present, and during short wave ripples at rest, when replay takes place. However, we find a subset of pyramidal cells that are preferably active during rest, in the absence of theta oscillations and short wave ripples. We recorded these cells using two-photon imaging in dorsal CA1 of the hippocampus of mice, during a virtual reality object location recognition task. During locomotion, the cells show a similar level of activity as control cells, but their activity increases during rest, when this

Neuronal computations are matched to optimally encode the sensory information that is available and relevant for the animal. However, the physical distribution of sensory information is often shaped by the animal’s own behavior. One prominent example is the encoding of optic flow fields that are generated during self-motion of the animal and will therefore depend on the type of locomotion. How evolution has matched computational resources to the behavioral constraints of an animal is not known. Here we use in vivo two photon imaging to record from a population of >3.500 local-direction selecti

Neural computations occurring simultaneously in multiple cerebral cortical regions are critical for mediating behaviors. Progress has been made in understanding how neural activity in specific cortical regions contributes to behavior. However, there is a lack of tools that allow simultaneous monitoring and perturbing neural activity from multiple cortical regions. We have engineered a suite of technologies to enable easy, robust access to much of the dorsal cortex of mice for optical and electrophysiological recordings. First, I will describe microsurgery robots that can programmed to perform

Sequential temporal ordering and patterning are key features of natural signals, used by the brain to decode stimuli and perceive them as sensory objects. Touch is one sensory modality where temporal patterning carries key information, and the rodent whisker system is a prominent model for understanding neuronal coding and plasticity underlying touch sensation. Neurons in this system are precise encoders of fluctuations in whisker dynamics down to a timescale of milliseconds, but it is not clear whether they can refine their encoding abilities as a result of learning patterned stimuli. For exa

The neurons in our brain never function in isolation; they are organized into complex circuits which perform highly specialized information processing tasks and transfer information through large neuronal networks. The aim of Janelle Pakan's research group is to better understand how neural circuits function during the transformation of information from sensory perception to behavioural output. Importantly, they also aim to further understand the cell-type specific processes that interrupt the flow of information through neural circuits in neurodegenerative disorders with dementia. The Pakan

Memory deficits are a debilitating symptom of epilepsy, but little is known about mechanisms underlying cognitive deficits. Here, we describe a Na+ channel-dependent mechanism underlying altered hippocampal dendritic integration, degraded place coding, and deficits in spatial memory. Two-photon glutamate uncaging experiments revealed that the mechanisms constraining the generation of Na+ spikes in hippocampal 1st order pyramidal cell dendrites are profoundly degraded in experimental epilepsy. This phenomenon was reversed by selectively blocking Nav1.3 sodium channels. In-vivo two-photon imagin

Behavior varies even among genetically identical animals raised in the same environment. However, little is known about the circuit or anatomical underpinnings of this individuality, though previous work implicates sensory periphery. Drosophila olfaction presents an ideal model to study the biological basis of behavioral individuality, because while the neural circuit underlying olfactory behavior is well-described and highly stereotyped, persistent idiosyncrasy in behavior, neural coding, and neural wiring have also been described. Projection neurons (PNs), which relay odor signals sensed by

behaviour varies even among genetically identical animals raised in the same environment. However, little is known about the circuit or anatomical underpinnings of this individuality, though previous work implicates sensory periphery. Drosophila olfaction presents an ideal model to study the biological basis of behavioural individuality, because while the neural circuit underlying olfactory behaviour is well-described and highly stereotyped, persistent idiosyncrasy in behaviour, neural coding, and neural wiring have also been described. Projection neurons (PNs), which relay odor signals sensed

Many visual systems can process information in dynamically changing environments. In general, visual perception scales with changes in the visual stimulus, or contrast, irrespective of background illumination. This is achieved by adaptation. However, visual perception is challenged when adaptation is not fast enough to deal with sudden changes in overall illumination, for example when gaze follows a moving object from bright sunlight into a shaded area. We have recently shown that the visual system of the fly found a solution by propagating a corrective luminance-sensitive signal to higher pro

Animals rely on an internal sense of body position and movement to effectively control motor behaviour. This sense of proprioception is mediated by diverse populations of internal mechanosensory neurons distributed throughout the body. My lab is trying to understand how proprioceptive stimuli are detected by sensory neurons, integrated and transformed in central circuits, and used to guide motor output. We approach these questions using genetic tools, in vivo two-photon imaging, and patch-clamp electrophysiology in Drosophila. We recently found that the axons of fly leg proprioceptors are o

Brain-wide neuromodulation by behavioral variables, such as locomotion, pupil area, and face motion, have been observed in mice (Stringer et al., 2019; Musall et al., 2019). To study this mechanism at higher spatial resolution, we used two-photon imaging that allows recording of individual neuronal and synaptic bouton activity in mouse primary visual cortex (V1), while the animal's face was simultaneously videotaped. We aim to understand how face motion is related to the population activity of both cortical neurons and their lateral geniculate nucleus (LGN) afferents, during both visual stimul

An animal’s ability to respond to its environment relies on effectively decoding neural representations of sensory stimuli. While it is known that primary sensory cortices represent sensory stimuli through specific patterns of activity, it is unknown how these representations are preserved over time. Many primary and higher order cortices have been shown to exhibit changes in neural activity representing the same sensory stimuli even when behavior is stable, a process dubbed ‘representational drift’. This poses a critical challenge for the brain – how can animals maintain stable perception and

Long-term potentiation (LTP) at hippocampal CA3-CA1 synapses, can be subdivided into two mechanistically different forms of NMDAR-dependent synaptic potentiation based on their independence of (LTP1) or dependence on (LTP2) de novo protein synthesis (PS). Previous experiments reported the requirement of CP-AMPAR activation and intracellular calcium stores for LTP2 but not LTP11,2. Here the requirement for CP-AMPARs and intracellular calcium stores in structural LTP (sLTP) were investigated. Simultaneous field potential recordings and two-photon imaging were carried out in acute hippocampal sli