Cooperative thalamocortical circuit mechanism for sensory prediction errors.

The brain functions as a prediction machine, utilizing an internal model of the world to anticipate sensations and the outcomes of our actions. Discrepancies between expected and actual events, referred to as prediction errors, are leveraged to update the internal model and guide our attention towards unexpected events1-10. Despite the importance of prediction-error signals for various neural computations across the brain, surprisingly little is known about the neural circuit mechanisms responsible for their implementation. Here we describe a thalamocortical disinhibitory circuit that is required for generating sensory prediction-error signals in mouse primary visual cortex (V1). We show that violating animals' predictions by an unexpected visual stimulus preferentially boosts responses of the layer 2/3 V1 neurons that are most selective for that stimulus. Prediction errors specifically amplify the unexpected visual input, rather than representing non-specific surprise or difference signals about how the visual input deviates from the animal's predictions. This selective amplification is implemented by a cooperative mechanism requiring thalamic input from the pulvinar and cortical vasoactive-intestinal-peptide-expressing (VIP) inhibitory interneurons. In response to prediction errors, VIP neurons inhibit a specific subpopulation of somatostatin-expressing inhibitory interneurons that gate excitatory pulvinar input to V1, resulting in specific pulvinar-driven response amplification of the most stimulus-selective neurons in V1. Therefore, the brain prioritizes unpredicted sensory information by selectively increasing the salience of unpredicted sensory features through the synergistic interaction of thalamic input and neocortical disinhibitory circuits.

A multicolor suite for deciphering population coding of calcium and cAMP in vivo.

cAMP is a universal second messenger regulated by various upstream pathways including Ca2+ and G-protein-coupled receptors (GPCRs). To decipher in vivo cAMP dynamics, we rationally designed cAMPinG1, a sensitive genetically encoded green cAMP indicator that outperformed its predecessors in both dynamic range and cAMP affinity. Two-photon cAMPinG1 imaging detected cAMP transients in the somata and dendritic spines of neurons in the mouse visual cortex on the order of tens of seconds. In addition, multicolor imaging with a sensitive red Ca2+ indicator RCaMP3 allowed simultaneous measurement of population patterns in Ca2+ and cAMP in hundreds of neurons. We found Ca2+-related cAMP responses that represented specific information, such as direction selectivity in vision and locomotion, as well as GPCR-related cAMP responses. Overall, our multicolor suite will facilitate analysis of the interaction between the Ca2+, GPCR and cAMP signaling at single-cell resolution both in vitro and in vivo.

Dual-polarity voltage imaging of the concurrent dynamics of multiple neuron types.

Genetically encoded fluorescent voltage indicators are ideally suited to reveal the millisecond-scale interactions among and between targeted cell populations. However, current indicators lack the requisite sensitivity for in vivo multipopulation imaging. We describe next-generation green and red voltage sensors, Ace-mNeon2 and VARNAM2, and their reverse response-polarity variants pAce and pAceR. Our indicators enable 0.4- to 1-kilohertz voltage recordings from >50 spiking neurons per field of view in awake mice and ~30-minute continuous imaging in flies. Using dual-polarity multiplexed imaging, we uncovered brain state-dependent antagonism between neocortical somatostatin-expressing (SST+) and vasoactive intestinal peptide-expressing (VIP+) interneurons and contributions to hippocampal field potentials from cell ensembles with distinct axonal projections. By combining three mutually compatible indicators, we performed simultaneous triple-population imaging. These approaches will empower investigations of the dynamic interplay between neuronal subclasses at single-spike resolution.

Neurovascular coupling and oxygenation are decreased in hippocampus compared to neocortex because of microvascular differences.

The hippocampus is essential for spatial and episodic memory but is damaged early in Alzheimer's disease and is very sensitive to hypoxia. Understanding how it regulates its oxygen supply is therefore key for designing interventions to preserve its function. However, studies of neurovascular function in the hippocampus in vivo have been limited by its relative inaccessibility. Here we compared hippocampal and visual cortical neurovascular function in awake mice, using two photon imaging of individual neurons and vessels and measures of regional blood flow and haemoglobin oxygenation. We show that blood flow, blood oxygenation and neurovascular coupling were decreased in the hippocampus compared to neocortex, because of differences in both the vascular network and pericyte and endothelial cell function. Modelling oxygen diffusion indicates that these features of the hippocampal vasculature may restrict oxygen availability and could explain its sensitivity to damage during neurological conditions, including Alzheimer's disease, where the brain's energy supply is decreased.

Spatial connectivity matches direction selectivity in visual cortex.

The selectivity of neuronal responses arises from the architecture of excitatory and inhibitory connections. In the primary visual cortex, the selectivity of a neuron in layer 2/3 for stimulus orientation and direction is thought to arise from intracortical inputs that are similarly selective1-8. However, the excitatory inputs of a neuron can have diverse stimulus preferences1-4,6,7,9, and inhibitory inputs can be promiscuous10 and unselective11. Here we show that the excitatory and inhibitory intracortical connections to a layer 2/3 neuron accord with its selectivity by obeying precise spatial patterns. We used rabies tracing1,12 to label and functionally image the excitatory and inhibitory inputs to individual pyramidal neurons of layer 2/3 of the mouse visual cortex. Presynaptic excitatory neurons spanned layers 2/3 and 4 and were distributed coaxial to the preferred orientation of the postsynaptic neuron, favouring the region opposite to its preferred direction. By contrast, presynaptic inhibitory neurons resided within layer 2/3 and favoured locations near the postsynaptic neuron and ahead of its preferred direction. The direction selectivity of a postsynaptic neuron was unrelated to the selectivity of presynaptic neurons, but correlated with the spatial displacement between excitatory and inhibitory presynaptic ensembles. Similar asymmetric connectivity establishes direction selectivity in the retina13-17. This suggests that this circuit motif might be canonical in sensory processing.

Ocular dominance plasticity: Molecular mechanisms revisited.

Ocular dominance plasticity (ODP) is a type of cortical plasticity operating in visual cortex of mammals that are endowed with binocular vision based on the competition-driven disparity. Earlier, a molecular mechanism was proposed that catecholamines play an important role in the maintenance of ODP in kittens. Having survived the initial test, the hypothesis was further advanced to identify noradrenaline (NA) as a key factor that regulates ODP in the immature cortex. Later, the ODP-promoting effect of NA is extended to the adult with age-related limitations. Following the enhanced NA availability, the chain events downstream lead to the ß-adrenoreceptor-induced cAMP accumulation, which in turn activates the protein kinase A. Eventually, the protein kinase translocates to the cell nucleus to activate cAMP responsive element binding protein (CREB). CREB is a cellular transcription factor that controls the transcription of various genes, underpinning neuronal plasticity and long-term memory. In the advent of molecular genetics in that various types of new tools have become available with relative ease, ODP research has lightly adopted in the rodent model the original concepts and methodologies. Here, after briefly tracing the strategic maturation of our quest, the review moves to the later development of the field, with the emphasis placed around the following issues: (a) Are we testing ODP per se? (b) What does monocular deprivation deprive of the immature cortex? (c) The critical importance of binocular competition, (d) What is the adult plasticity? (e) Excitation-Inhibition balance in local circuits, and (f) Species differences in the animal models.

Updating the picture of layer 2/3 VIP-expressing interneuron function in the mouse cerebral cortex.

For years, interneurons expressing vasoactive intestinal peptide (VIP) interneurons and their function within the neocortex have been shrouded in mystery. Their relatively small size and minimal representation in the cortex have made investigation difficult. Due to their service role performed in co­operation with glia and blood vessels to supply energy during neuronal activation in the brain, the contribution of VIP interneurons to local neuronal circuit function was not appreciated. VIP interneurons in the neocortex account for roughly 12% of all interneurons. They have been described as a subgroup of the third largest population of 5-hydroxytryptamine 3a (5HT3a) receptor­expressing interneurons, non­overlapping with interneuron populations expressing parvalbumin (PV) or somatostatin (SST). However, it was recently shown that only half of VIP interneurons display a 5HT3a receptor response and a subset of VIP interneurons in visual cortex co­express SST. Over the last several years, due to new technical advancements, many facts have emerged relating to VIP interneuron phylogenetic origin, operational mechanisms within local circuits and functional significance. Some of these discoveries have dramatically shifted the perception of VIP interneurons. This review focuses on the function of the VIP interneurons residing in layer 2/3 of the mouse neocortex.

Xenotransplanted Human Cortical Neurons Reveal Species-Specific Development and Functional Integration into Mouse Visual Circuits.

How neural circuits develop in the human brain has remained almost impossible to study at the neuronal level. Here, we investigate human cortical neuron development, plasticity, and function using a mouse/human chimera model in which xenotransplanted human cortical pyramidal neurons integrate as single cells into the mouse cortex. Combined neuronal tracing, electrophysiology, and in vivo structural and functional imaging of the transplanted cells reveal a coordinated developmental roadmap recapitulating key milestones of human cortical neuron development. The human neurons display a prolonged developmental timeline, indicating the neuron-intrinsic retention of juvenile properties as an important component of human brain neoteny. Following maturation, human neurons in the visual cortex display tuned, decorrelated responses to visual stimuli, like mouse neurons, demonstrating their capacity for physiological synaptic integration in host cortical circuits. These findings provide new insights into human neuronal development and open novel avenues for the study of human neuronal function and disease. VIDEO ABSTRACT.

Energy-efficient information transfer at thalamocortical synapses.

We have previously shown that the physiological size of postsynaptic currents maximises energy efficiency rather than information transfer across the retinothalamic relay synapse. Here, we investigate information transmission and postsynaptic energy use at the next synapse along the visual pathway: from relay neurons in the thalamus to spiny stellate cells in layer 4 of the primary visual cortex (L4SS). Using both multicompartment Hodgkin-Huxley-type simulations and electrophysiological recordings in rodent brain slices, we find that increasing or decreasing the postsynaptic conductance of the set of thalamocortical inputs to one L4SS cell decreases the energy efficiency of information transmission from a single thalamocortical input. This result is obtained in the presence of random background input to the L4SS cell from excitatory and inhibitory corticocortical connections, which were simulated (both excitatory and inhibitory) or injected experimentally using dynamic-clamp (excitatory only). Thus, energy efficiency is not a unique property of strong relay synapses: even at the relatively weak thalamocortical synapse, each of which contributes minimally to the output firing of the L4SS cell, evolutionarily-selected postsynaptic properties appear to maximise the information transmitted per energy used.

Neuronal cell-subtype specificity of neural synchronization in mouse primary visual cortex.

Spatiotemporally synchronised neuronal activity is central to sensation, motion and cognition. Brain circuits consist of dynamically interconnected neuronal cell-types, thus elucidating how neuron types synergise within the network is key to understand the neuronal orchestra. Here we show that in neocortex neuron-network coupling is neuronal cell-subtype specific. Employing in vivo two-photon (2-p) Calcium (Ca) imaging and 2-p targeted whole-cell recordings, we cell-type specifically investigated the coupling profiles of genetically defined neuron populations in superficial layers (L) of mouse primary visual cortex (V1). Our data reveal novel subtlety of neuron-network coupling in inhibitory interneurons (INs). Parvalbumin (PV)- and Vasoactive intestinal peptide (VIP)-expressing INs exhibit skewed distributions towards strong network-coupling; in Somatostatin (SST)-expressing INs, however, two physiological subpopulations are identified with distinct neuron-network coupling profiles, providing direct evidence for subtype specificity. Our results thus add novel functional granularity to neuronal cell-typing, and provided insights critical to simplifying/understanding neural dynamics.

Synapse-Selective Control of Cortical Maturation and Plasticity by Parvalbumin-Autonomous Action of SynCAM 1.

Cortical plasticity peaks early in life and tapers in adulthood, as exemplified in the primary visual cortex (V1), wherein brief loss of vision in one eye reduces cortical responses to inputs from that eye during the critical period but not in adulthood. The synaptic locus of cortical plasticity and the cell-autonomous synaptic factors determining critical periods remain unclear. We here demonstrate that the immunoglobulin protein Synaptic Cell Adhesion Molecule 1 (SynCAM 1/Cadm1) is regulated by visual experience and limits V1 plasticity. Loss of SynCAM 1 selectively reduces the number of thalamocortical inputs onto parvalbumin (PV+) interneurons, impairing the maturation of feedforward inhibition in V1. SynCAM 1 acts in PV+ interneurons to actively restrict cortical plasticity, and brief PV+-specific knockdown of SynCAM 1 in adult visual cortex restores juvenile-like plasticity. These results identify a synapse-specific, cell-autonomous mechanism for thalamocortical visual circuit maturation and closure of the visual critical period.

Time course of cytochrome oxidase blob plasticity in the primary visual cortex of adult monkeys after retinal laser lesions.

We studied the time course of changes of cytochrome oxidase (CytOx) blob spatial density and blob cross-sectional area of deprived (D) and nondeprived (ND) portions of V1 in four capuchin monkeys after massive and restricted retinal laser lesions. Laser shots at the border of the optic disc produced massive retinal lesions, while low power laser shots in the retina produced restricted retinal lesions. These massive and restricted retinal lesions were intended to simulate glaucoma and diabetic retinopathy, respectively. We used a Neodymium-YAG dual frequency laser to make the lesions. We measured Layer III blobs in CytOx-reacted tangential sections of flat-mounted preparations of V1. The plasticity of the blob system and that of the ocular dominance columns (ODC) varied with the degree of retinal lesions. We found that changes in the blob system were different from that of the ODC. Blob sizes changed drastically in the region corresponding to the retinal lesion. Blobs were larger and subjectively darker above and below the non deprived ODC than in the deprived columns. With restricted lesions, blobs corresponding to the ND columns had sizes similar to those from non-lesioned areas. In contrast, blobs corresponding to the deprived columns were smaller than those from nonlesioned areas. With massive lesions, ND blobs were larger than the deprived blobs. Plastic changes in blobs described here occur much earlier than previously described.

A characterization of laminar architecture in mouse primary auditory cortex.

Laminar architecture of primary auditory cortex (A1) has long been investigated by traditional histochemical techniques such as Nissl staining, retrograde and anterograde tracings. Uncertainty still remains, however, about laminar boundaries in mice. Here we investigated the cortical lamina structure by combining neuronal tracing and immunofluorochemistry for laminar specific markers. Most retrogradely labeled corticothalamic neurons expressed Forkhead box protein P2 (Foxp2) and distributed within the laminar band of Foxp2-expressing cells, identifying layer 6. Cut-like homeobox 1 (Cux1) expression in layer 2-4 neurons divided the upper layers into low expression layers 2/3 and high expression layers 3/4, which overlapped with the dense terminals of vesicular glutamate transporter 2 (vGluT2) and anterogradely labeled lemniscal thalamocortical axons. In layer 5, between Cux1-expressing layers 2-4 and Foxp2-defined layer 6, retrogradely labeled corticocollicular projection neurons mostly expressed COUP-TF interacting protein 2 (Ctip2). Ctip2-expressing neurons formed a laminar band in the middle of layer 5 distant from layer 6, creating a laminar gap between the two laminas. This gap contained a high population of commissural neurons projecting to contralateral A1 compared to other layers and received vGluT2-immunopositive, presumptive thalamocortical axon collateral inputs. Our study shows that layer 5 is much wider than layer 6, and layer 5 can be divided into at least three sublayers. The thalamorecipient layers 3/4 may be separated from layers 2/3 using Cux1 and can be also divided into layer 4 and layer 3 based on the neuronal soma size. These data provide a new insight for the laminar structure of mouse A1.

Laminar specific gene expression reveals differences in postnatal laminar maturation in mouse auditory, visual, and somatosensory cortex.

Proper formation of laminar structures in sensory cortexes is critical for sensory information processing. Previous studies suggested that the timing of neuronal migration and the laminar position of cortical neurons differ among sensory cortexes. How they differ during postnatal development has not been systematically investigated. Here, identifying laminas using transcription factors, we examined postnatal changes in neuronal density and distribution in presumptive primary auditory (ACx), visual (VCx), and somatosensory cortexes (SCx) in a strain of mice using immunofluorescence techniques. Development of laminar thickness and its cortical proportion differed among the sensory cortexes. Layers 2-4 defined by Cut-like homeobox 1 (Cux1)-expressing neurons were narrower, and layer 5 was wider in ACx compared to those in VCx or SCx, while Forkhead-box protein P2 (Foxp2)-defined layer 6 was wider in SCx than the other two sensory cortexes throughout postnatal development. Meanwhile, thalamocortical input layers identified by Cux1-expressing neurons formed later in ACx than in the other two cortical regions. The cell densities of ETS-related protein 81-expressing neurons increased in both lower and upper layers but at distinct timing, while those of COUP-TF-interacting protein 2 expressing neurons in the lower layers changed bidirectionally (i.e., increased or decreased) both in layer- and cortical region-specific manners. Foxp2-expressing cells in layer 6 distributed differently and declined at different timing among the sensory cortexes. Overall, we demonstrate that the maturational timing of lamina differs among the sensory cortexes and that postnatal age-dependent changes in neuronal distribution are unique to each of the sensory cortexes.

Visual Processing by Calretinin Expressing Inhibitory Neurons in Mouse Primary Visual Cortex.

Inhibition in the cerebral cortex is delivered by a variety of GABAergic interneurons. These cells have been categorized by their morphology, physiology, gene expression and connectivity. Many of these classes appear to be conserved across species, suggesting that the classes play specific functional roles in cortical processing. What these functions are, is still largely unknown. The largest group of interneurons in the upper layers of mouse primary visual cortex (V1) is formed by cells expressing the calcium-binding protein calretinin (CR). This heterogeneous class contains subsets of vasoactive intestinal polypeptide (VIP) interneurons and somatostatin (SOM) interneurons. Here we show, using in vivo two-photon calcium imaging in mice, that CR neurons can be sensitive to stimulus orientation, but that they are less selective on average than the overall neuronal population. Responses of CR neurons are suppressed by a surrounding stimulus, but less so than the overall population. In rats and primates, CR interneurons have been suggested to provide disinhibition, but we found that in mice their in vivo activation by optogenetics causes a net inhibition of cortical activity. Our results show that the average functional properties of CR interneurons are distinct from the averages of the parvalbumin, SOM and VIP interneuron populations.

Fibroblast Growth Factor 9 Suppresses Striatal Cell Death Dominantly Through ERK Signaling in Huntington's Disease.

BACKGROUND/AIMS: Huntington's disease (HD) is a heritable neurodegenerative disorder, and there is no cure for HD to date. A type of fibroblast growth factor (FGF), FGF9, has been reported to play prosurvival roles in other neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. However, the effects of FGF9 on HD is still unknown. With many similarities in the cellular and pathological mechanisms that eventually cause cell death in neurodegenerative diseases, we hypothesize that FGF9 might provide neuroprotective functions in HD. METHODS: In this study, STHdhQ7/Q7 (WT) and STHdhQ111/Q111 (HD) striatal knock-in cell lines were used to evaluate the neuroprotective effects of FGF9. Cell proliferation, cell death and neuroprotective markers were determined via the MTT assay, propidium iodide staining and Western blotting, respectively. The signaling pathways regulated by FGF9 were demonstrated using Western blotting. Additionally, HD transgenic mouse models were used to further confirm the neuroprotective effects of FGF9 via ELISA, Western blotting and immunostaining. RESULTS: Results show that FGF9 not only enhances cell proliferation, but also alleviates cell death as cells under starvation stress. In addition, FGF9 significantly upregulates glial cell line-derived neurotrophic factor (GDNF) and an anti-apoptotic marker, Bcl-xL, and decreases the expression level of an apoptotic marker, cleaved caspase 3. Furthermore, FGF9 functions through ERK, AKT and JNK pathways. Especially, ERK pathway plays a critical role to influence the effects of FGF9 toward cell survival and GDNF production. CONCLUSIONS: These results not only show the neuroprotective effects of FGF9, but also clarify the critical mechanisms in HD cells, further providing an insight for the therapeutic potential of FGF9 in HD.

Distinct learning-induced changes in stimulus selectivity and interactions of GABAergic interneuron classes in visual cortex.

How learning enhances neural representations for behaviorally relevant stimuli via activity changes of cortical cell types remains unclear. We simultaneously imaged responses of pyramidal cells (PYR) along with parvalbumin (PV), somatostatin (SOM), and vasoactive intestinal peptide (VIP) inhibitory interneurons in primary visual cortex while mice learned to discriminate visual patterns. Learning increased selectivity for task-relevant stimuli of PYR, PV and SOM subsets but not VIP cells. Strikingly, PV neurons became as selective as PYR cells, and their functional interactions reorganized, leading to the emergence of stimulus-selective PYR-PV ensembles. Conversely, SOM activity became strongly decorrelated from the network, and PYR-SOM coupling before learning predicted selectivity increases in individual PYR cells. Thus, learning differentially shapes the activity and interactions of multiple cell classes: while SOM inhibition may gate selectivity changes, PV interneurons become recruited into stimulus-specific ensembles and provide more selective inhibition as the network becomes better at discriminating behaviorally relevant stimuli.

Core Differences in Synaptic Signaling Between Primary Visual and Dorsolateral Prefrontal Cortex.

Neurons in primary visual cortex (V1) are more resilient than those in dorsolateral prefrontal cortex (dlPFC) in aging, schizophrenia and Alzheimer's disease. The current study compared glutamate and neuromodulatory actions in macaque V1 to those in dlPFC, and found striking regional differences. V1 neuronal firing to visual stimuli depended on AMPA receptors, with subtle NMDA receptor contributions, while dlPFC depends primarily on NMDA receptors. Neuromodulatory actions also differed between regions. In V1, cAMP signaling increased neuronal firing, and the phosphodiesterase PDE4A was positioned to regulate cAMP effects on glutamate release from axons. HCN channels in V1 were classically located on distal dendrites, and enhanced cell firing. These data contrast with dlPFC, where PDE4A and HCN channels are concentrated in thin spines, and cAMP-HCN signaling gates inputs and weakens firing. These regional differences may explain why V1 neurons are more resilient than dlPFC neurons to the challenges of age and disease.

CD38 is Required for Dendritic Organization in Visual Cortex and Hippocampus.

Morphological screening of mouse brains with known behavioral deficits can give great insight into the relationship between brain regions and their behavior. Oxytocin- and CD38-deficient mice have previously been shown to have behavioral phenotypes, such as restrictions in social memory, social interactions, and maternal behavior. CD38 is reported as an autism spectrum disorder (ASD) candidate gene and its behavioral phenotypes may be linked to ASD. To address whether these behavioral phenotypes relate to brain pathology and neuronal morphology, here we investigate the morphological changes in the CD38-deficient mice brains, with focus on the pathology and neuronal morphology of the cortex and hippocampus, using Nissl staining, immunohistochemistry, and Golgi staining. No difference was found in terms of cortical layer thickness. However, we found abnormalities in the number of neurons and neuronal morphology in the visual cortex and dentate gyrus (DG). In particular, there were arborisation differences between CD38-/- and CD38+/+ mice in the apical dendrites of the visual cortex and hippocampal CA1 pyramidal neurons. The data suggest that CD38 is implicated in appropriate development of brain regions important for social behavior.