Optogenetic-guided cortical plasticity after nerve injury

Reactivated thalamocortical plasticity alters neural activity in sensory-motor cortex during post-critical period

Neuroplasticity in sensory brain areas supports adaptation after nerve injury and fundamentally impacts sensation and movement. However, limited neuroplasticity in somatosensory areas due to the early critical period makes determining the role of thalamocortical (TC) inputs in sensorimotor signal processing challenging. Here, we demonstrated that reactivation of TC neuroplasticity was associated with an increase in the number of neurons in layer IV (L4) of the whisker primary somatosensory cortex (wS1) with a stable excitation-inhibition ratio. Highly synchronized neural activity in L4 propagated throughout the wS1 column and to the downstream areas, including whisker secondary somatosensory, primary motor cortices, and contralateral wS1. These results provide crucial evidence that TC inputs can alter the neural activity of sensory-motor pathways even after the critical period. Altogether, these enormous changes in sensorimotor circuit activity are important for adaptation following an injury such as limb loss, stroke, or other forms of neural injury.

Magnetogenetic stimulation inside MRI induces spontaneous and evoked changes in neural circuits activity in rats

The ability to modulate specific neural circuits and simultaneously visualize and measure brain activity with MRI would greatly impact our understanding of brain function in health and disease. The combination of neurostimulation methods and functional MRI in animal models have already shown promise in elucidating fundamental mechanisms associated with brain activity. We developed an innovative magnetogenetics neurostimulation technology that can trigger neural activity through magnetic fields. Similar to other genetic-based neuromodulation methods, magnetogenetics offers cell-, area-, and temporal-specific control of neural activity. The magnetogenetic protein-Electromagnetic Perceptive Gene (EPG)-is activated by non-invasive magnetic fields, providing a unique way to target neural circuits by the MRI static and gradient fields while simultaneously measuring their effect on brain activity. EPG was expressed in rat's visual cortex and the amplitude of low-frequency fluctuation, resting-state functional connectivity (FC), and sensory activation was measured using a 7T MRI. The results demonstrate that EPG-expressing rats had significantly higher signal fluctuations in the visual areas and stronger FC in sensory areas consistent with known anatomical visuosensory and visuomotor connections. This new technology complements the existing neurostimulation toolbox and provides a means to study brain function in a minimally-invasive way which was not possible previously.

Cortical Reorganization after Limb Loss: Bridging the Gap between Basic Science and Clinical Recovery

Despite the increasing incidence and prevalence of amputation across the globe, individuals with acquired limb loss continue to struggle with functional recovery and chronic pain. A more complete understanding of the motor and sensory remodeling of the peripheral and central nervous system that occurs postamputation may help advance clinical interventions to improve the quality of life for individuals with acquired limb loss. The purpose of this article is to first provide background clinical context on individuals with acquired limb loss and then to provide a comprehensive review of the known motor and sensory neural adaptations from both animal models and human clinical trials. Finally, the article bridges the gap between basic science researchers and clinicians that treat individuals with limb loss by explaining how current clinical treatments may restore function and modulate phantom limb pain using the underlying neural adaptations described above. This review should encourage the further development of novel treatments with known neurological targets to improve the recovery of individuals postamputation.Significance Statement In the United States, 1.6 million people live with limb loss; this number is expected to more than double by 2050. Improved surgical procedures enhance recovery, and new prosthetics and neural interfaces can replace missing limbs with those that communicate bidirectionally with the brain. These advances have been fairly successful, but still most patients experience persistent problems like phantom limb pain, and others discontinue prostheses instead of learning to use them daily. These problematic patient outcomes may be due in part to the lack of consensus among basic and clinical researchers regarding the plasticity mechanisms that occur in the brain after amputation injuries. Here we review results from clinical and animal model studies to bridge this clinical-basic science gap.

Magnetogenetic stimulation inside MRI induces spontaneous and evoked changes in neural circuits activity in rats

The ability to modulate specific neural circuits and simultaneously visualize and measure brain activity with MRI would greatly impact understanding brain function in health and disease. The combination of neurostimulation methods and MRI in animal models have already shown promise in elucidating fundamental mechanisms associated with brain activity. We developed an innovative magnetogenetics neurostimulation technology that can trigger neural activity through magnetic fields. Similar to other genetic-based neuromodulation methods, magnetogenetics offers cell-, area- and temporal-specific control of neural activity. However, the magnetogenetics protein (Electromagnetic Preceptive Gene (EPG)) are activated by non-invasive magnetic fields, providing a unique way to target neural circuits by the MRI gradients while simultaneously measure their effect on brain activity. EPG was expressed in rat's visual cortex and the amplitude of low-frequency fluctuation (fALFF), resting-state functional connectivity (FC), and sensory activation was measured using a 7T MRI. The results demonstrate that EPG-expressing rats had significantly higher signal fluctuations in the visual areas and stronger FC in sensory areas consistent with known anatomical visuosensory and visuomotor connections. This new technology complements the existing neurostimulation toolbox and provides a mean to study brain function in a minimally-invasive way which was not possible previously.

Closed-loop neurostimulation via expression of magnetogenetics-sensitive protein in inhibitory neurons leads to reduction of seizure activity in a rat model of epilepsy

On-demand neurostimulation has shown success in epilepsy patients with pharmacoresistant seizures. Seizures produce magnetic fields that can be recorded using magnetoencephalography. We developed a new closed-loop approach to control seizure activity based on magnetogenetics using the electromagnetic perceptive gene (EPG) that encodes a protein that responds to magnetic fields. The EPG transgene was expressed in inhibitory interneurons under the hDlx promoter and kainic acid was used to induce acute seizures. In vivo electrophysiological signals were recorded. We found that hDlx EPG rats exhibited a significant delay in the onset of first seizure (1142.72 ± 186.35 s) compared to controls (644.03 ± 15.06 s) and significantly less seizures (4.11 ± 1.03) compared to controls (8.33 ± 1.58). These preliminary findings suggest that on-demand activation of EPG expressed in inhibitory interneurons suppresses seizure activity, and magnetogenetics via EPG may be an effective strategy to alleviate seizure severity in a closed-loop, and cell-specific fashion.

Reorganization of sensorimotor representations of the intact limb after upper but not lower limb traumatic amputation

It is becoming increasingly clear that limb loss induces wider spread reorganization of representations of the body that are nonadjacent to the affected cortical territory. Data from upper extremity amputees reveal intrusion of the representation of the ipsilateral intact limb into the former hand territory. Here we test for the first time whether this reorganization of the intact limb into the deprived cortex is specific to the neurological organization of the upper limbs or reflects large scale adaptation that is triggered by any unilateral amputation. BOLD activity was measured as human subjects with upper limb and lower limb traumatic amputation and their controls moved the toes on each foot, open and closed each hand and pursed their lips. Subjects with amputation were asked to imagine moving the missing limb while remaining still. Bayesian pattern component modeling of fMRI data showed that intact ipsilateral movements and contralateral movements of the hand and foot were distinctly represented in the deprived sensorimotor cortex years after upper limb amputation. In contrast, there was evidence reminiscent of contralateral specificity for hand and foot movements following lower limb amputation, like that seen in controls. We propose the cortical reorganization of the intact limb to be a function of use-dependent plasticity that is more specific to the consequence of upper limb loss of forcing an asymmetric reliance on the intact hand and arm. The contribution of this reorganization to phantom pain or a heightened risk of overuse and resultant maladaptive plasticity needs investigating before targeting such reorganization in intervention.

Cortical reintegration after facial allotransplantation

Neural plasticity of the brain or its ability to reorganize following injury has likely coincided with the successful clinical correction of severe deformity by facial transplantation since 2005. In this study, we present the cortical reintegration outcomes following syngeneic hemifacial vascularized composite allograft (VCA) in a small animal model. Specifically, changes in the topographic organization and unit response properties of the rodent whisker-barrel somatosensory system were assessed following hemifacial VCA. Clear differences emerged in the barrel-cortex system when comparing naïve and hemiface transplanted animals. Neurons in the somatosensory cortex of transplanted rats had decreased sensitivity albeit increased directional sensitivity compared with naïve rats and evoked responses in transplanted animals were more temporally dispersed. In addition, receptive fields were often topographically mismatched with the indication that the mismatched topography reorganized within adjacent barrel (same row-arc bias following hemifacial transplant). These results suggest subcortical changes in the thalamus and/or brainstem play a role in hemifacial transplantation cortical plasticity and demonstrate the discrete and robust data that can be derived from this clinically relevant small animal VCA model for use in optimizing postsurgical outcomes.NEW & NOTEWORTHY Robust rodent hemifacial transplant model was used to record functional changes in somatosensory cortex after transplantation. Neurons in the somatosensory cortex of face transplant recipients had decreased sensitivity to stimulation of whiskers with increased directional sensitivity vs. naive rats. Transplant recipient cortical unit response was more dispersed in temporary vs. naive rats. Despite histological similarities to naive cortices, transplant recipient cortices had a mix of topographically appropriate and inappropriate whiskered at barrel cortex relationships.

Peripheral Nerve Injury Induces Changes in the Activity of Inhibitory Interneurons as Visualized in Transgenic GAD1-GCaMP6s Rats

Peripheral nerve injury induces cortical remapping that can lead to sensory complications. There is evidence that inhibitory interneurons play a role in this process, but the exact mechanism remains unclear. Glutamate decarboxylase-1 (GAD1) is a protein expressed exclusively in inhibitory interneurons. Transgenic rats encoding GAD1–GCaMP were generated to visualize the activity in GAD1 neurons through genetically encoded calcium indicators (GCaMP6s) in the somatosensory cortex. Forepaw denervation was performed in adult rats, and fluorescent Ca2+ imaging on cortical slices was obtained. Local, intrahemispheric stimulation (cortical layers 2/3 and 5) induced a significantly higher fluorescence change of GAD1-expressing neurons, and a significantly higher number of neurons were responsive to stimulation in the denervated rats compared to control rats. However, remote, interhemispheric stimulation of the corpus callosum induced a significantly lower fluorescence change of GAD1-expressing neurons, and significantly fewer neurons were deemed responsive to stimulation within layer 5 in denervated rats compared to control rats. These results suggest that injury impacts interhemispheric communication, leading to an overall decrease in the activity of inhibitory interneurons in layer 5. Overall, our results provide direct evidence that inhibitory interneuron activity in the deprived S1 is altered after injury, a phenomenon likely to affect sensory processing.

fNIRS brain measures of ongoing nociception during surgical incisions under anesthesia

Significance: Functional near-infrared spectroscopy (fNIRS) has evaluated pain in awake and anesthetized states. Aim: We evaluated fNIRS signals under general anesthesia in patients undergoing knee surgery for anterior cruciate ligament repair. Approach: Patients were split into groups: those with regional nerve block (NB) and those without (non-NB). Continuous fNIRS measures came from three regions: the primary somatosensory cortex (S1), known to be involved in evaluation of nociception, the lateral prefrontal cortex (BA9), and the polar frontal cortex (BA10), both involved in higher cortical functions (such as cognition and emotion). Results: Our results show three significant differences in fNIRS signals to incision procedures between groups: (1) NB compared with non-NB was associated with a greater net positive hemodynamic response to pain procedures in S1; (2) dynamic correlation between the prefrontal cortex (PreFC) and S1 within 1 min of painful procedures are anticorrelated in NB while positively correlated in non-NB; and (3) hemodynamic measures of activation were similar at two separate time points during surgery (i.e., first and last incisions) in PreFC and S1 but showed significant differences in their overlap. Comparing pain levels immediately after surgery and during discharge from postoperative care revealed no significant differences in the pain levels between NB and non-NB. Conclusion: Our data suggest multiple pain events that occur during surgery using devised algorithms could potentially give a measure of "pain load." This may allow for evaluation of central sensitization (i.e., a heightened state of the nervous system where noxious and non-noxious stimuli is perceived as painful) to postoperative pain levels and the resulting analgesic consumption. This evaluation could potentially predict postsurgical chronic neuropathic pain.

Multi-session delivery of synchronous rTMS and sensory stimulation induces long-term plasticity

BACKGROUND

Combining training or sensory stimulation with non-invasive brain stimulation has shown to improve performance in healthy subjects and improve brain function in patients after brain injury. However, the plasticity mechanisms and the optimal parameters to induce long-term and sustainable enhanced performance remain unknown.

OBJECTIVE

This work was designed to identify the protocols of which combining sensory stimulation with repetitive transcranial magnetic stimulation (rTMS) will facilitate the greatest changes in fMRI activation maps in the rat's primary somatosensory cortex (S1).

METHODS

Several protocols of combining forepaw electrical stimulation with rTMS were tested, including a single stimulation session compared to multiple, daily stimulation sessions, as well as synchronous and asynchronous delivery of both modalities. High-resolution fMRI was used to determine how pairing sensory stimulation with rTMS induced short and long-term plasticity in the rat S1.

RESULTS

All groups that received a single session of rTMS showed short-term increases in S1 activity, but these increases did not last three days after the session. The group that received a stimulation protocol of 10 Hz forepaw stimulation that was delivered simultaneously with 10 Hz rTMS for five consecutive days demonstrated the greatest increases in the extent of the evoked fMRI responses compared to groups that received other stimulation protocols.

CONCLUSIONS

Our results provide direct indication that pairing peripheral stimulation with rTMS induces long-term plasticity, and this phenomenon appears to follow a time-dependent plasticity mechanism. These results will be important to lead the design of new training and rehabilitation paradigms and training towards achieving maximal performance in healthy subjects.

Comparison of the Efficacy of Optogenetic Stimulation of Glia versus Neurons in Myelination

Increasing evidence demonstrates that optogenetics contributes to the regulation of brain behavior, cognition, and physiology, particularly during myelination, potentially allowing for the bidirectional modulation of specific cell lines with spatiotemporal accuracy. However, the type of cell to be targeted, namely, glia vs neurons, and the degree to which optogenetically induced cell activity can regulate myelination during the development of the peripheral nervous system (PNS) are still underexplored. Herein, we report the comparison of optogenetic stimulation (OS) of Schwann cells (SCs) and motor neurons (MNs) for activation of myelination in the PNS. Capitalizing on these optogenetic tools, we confirmed that the formation of the myelin sheath was initially promoted more by OS of calcium translocating channelrhodopsin (CatCh)-transfected SCs than by OS of transfected MNs at 7 days in vitro (DIV). Additionally, the level of myelination was substantially enhanced even until 14 DIV. Surprisingly, after OS of SCs, > 91.1% ± 5.9% of cells expressed myelin basic protein, while that of MNs was 67.8% ± 6.1%. The potent effect of OS of SCs was revealed by the increased thickness of the myelin sheath at 14 DIV. Thus, the OS of SCs could highly accelerate myelination, while the OS of MNs only somewhat promoted myelination, indicating a clear direction for the optogenetic application of unique cell types for initiating and promoting myelination. Together, our findings support the importance of precise cell type selection for use in optogenetics, which in turn can be broadly applied to overcome the limitations of optogenetics after injury.

Non-invasive neuromodulation using rTMS and the electromagnetic-perceptive gene (EPG) facilitates plasticity after nerve injury

BACKGROUND

Twenty million Americans suffer from peripheral nerve injury. These patients often develop chronic pain and sensory dysfunctions. In the past decade, neuroimaging studies showed that these changes are associated with altered cortical excitation-inhibition balance and maladaptive plasticity. We tested if neuromodulation of the deprived sensory cortex could restore the cortical balance, and whether it would be effective in alleviating sensory complications.

OBJECTIVE

We tested if non-invasive repetitive transcranial magnetic stimulation (rTMS) which induces neuronal excitability, and cell-specific magnetic activation via the Electromagnetic-perceptive gene (EPG) which is a novel gene that was identified and cloned from glass catfish and demonstrated to evoke neural responses when magnetically stimulated, can restore cortical excitability.

METHODS

A rat model of forepaw denervation was used. rTMS was delivered every other day for 30 days, starting at the acute or at the chronic post-injury phase. A minimally-invasive neuromodulation via EPG was performed every day for 30 days starting at the chronic phase. A battery of behavioral tests was performed in the days and weeks following limb denervation in EPG-treated rats, and behavioral tests, fMRI and immunochemistry were performed in rTMS-treated rats.

RESULTS

The results demonstrate that neuromodulation significantly improved long-term mobility, decreased anxiety and enhanced neuroplasticity. The results identify that both acute and delayed rTMS intervention facilitated rehabilitation. Moreover, the results implicate EPG as an effective cell-specific neuromodulation approach.

CONCLUSION

Together, these results reinforce the growing amount of evidence from human and animal studies that are establishing neuromodulation as an effective strategy to promote plasticity and rehabilitation.

Enhancing plasticity in central networks improves motor and sensory recovery after nerve damage

Nerve damage can cause chronic, debilitating problems including loss of motor control and paresthesia, and generates maladaptive neuroplasticity as central networks attempt to compensate for the loss of peripheral connectivity. However, it remains unclear if this is a critical feature responsible for the expression of symptoms. Here, we use brief bursts of closed-loop vagus nerve stimulation (CL-VNS) delivered during rehabilitation to reverse the aberrant central plasticity resulting from forelimb nerve transection. CL-VNS therapy drives extensive synaptic reorganization in central networks paralleled by improved sensorimotor recovery without any observable changes in the nerve or muscle. Depleting cortical acetylcholine blocks the plasticity-enhancing effects of CL-VNS and consequently eliminates recovery, indicating a critical role for brain circuits in recovery. These findings demonstrate that manipulations to enhance central plasticity can improve sensorimotor recovery and define CL-VNS as a readily translatable therapy to restore function after nerve damage.

Peripheral nerve damage generates maladaptive neuroplasticity as central networks attempt to compensate for the loss of peripheral connectivity. Here, the authors reverse the aberrant plasticity via vagus nerve stimulation to elicit synaptic reorganization and to improve sensorimotor recovery.

Interhemispheric transfer of post-amputation cortical plasticity within the human somatosensory cortex

Animal models reveal that deafferenting forelimb injuries precipitate reorganization in both contralateral and ipsilateral somatosensory cortices. The functional significance and duration of these effects are unknown, and it is unclear whether they also occur in injured humans. We delivered cutaneous stimulation during functional magnetic resonance imaging (fMRI) to map the sensory cortical representation of the intact hand and lower face in a group of chronic, unilateral, upper extremity amputees (N = 19) and healthy matched controls (N = 29). Amputees exhibited greater activity than controls within the deafferented former sensory hand territory (S1f) during stimulation of the intact hand, but not of the lower face. Despite this cortical reorganization, amputees did not differ from controls in tactile acuity on their intact hands. S1f responses during hand stimulation were unrelated to tactile acuity, pain, prosthesis usage, or time since amputation. These effects appeared specific to the deafferented somatosensory modality, as fMRI visual mapping paradigm failed to detect any differences between groups. We conclude that S1f becomes responsive to cutaneous stimulation of the intact hand of amputees, and that this modality-specific reorganizational change persists for many years, if not indefinitely. The functional relevance of these changes, if any, remains unknown.

Multimodal Evaluation of TMS - Induced Somatosensory Plasticity and Behavioral Recovery in Rats With Contusion Spinal Cord Injury

Introduction: Spinal cord injury (SCI) causes partial or complete damage to sensory and motor pathways and induces immediate changes in cortical function. Current rehabilitative strategies do not address this early alteration, therefore impacting the degree of neuroplasticity and subsequent recovery. The following study aims to test if a non-invasive brain stimulation technique such as repetitive transcranial magnetic stimulation (rTMS) is effective in promoting plasticity and rehabilitation, and can be used as an early intervention strategy in a rat model of SCI. Methods: A contusion SCI was induced at segment T9 in adult rats. An rTMS coil was positioned over the brain to deliver high frequency stimulation. Behavior, motor and sensory functions were tested in three groups: SCI rats that received high-frequency (20 Hz) rTMS within 10 min post-injury (acute-TMS; n = 7); SCI rats that received TMS starting 2 weeks post-injury (chronic-TMS; n = 5), and SCI rats that received sham TMS (no-TMS, n = 5). Locomotion was evaluated by the Basso, Beattie, and Bresnahan (BBB) and gridwalk tests. Motor evoked potentials (MEP) were recorded from the forepaw across all groups to measure integrity of motor pathways. Functional MRI (fMRI) responses to contralateral tactile hindlimb stimulation were measured in an 11.7T horizontal bore small-animal scanner. Results: The acute-TMS group demonstrated the fastest improvements in locomotor performance in both the BBB and gridwalk tests compared to chronic and no-TMS groups. MEP responses from forepaw showed significantly greater difference in the inter-peak latency between acute-TMS and no-TMS groups, suggesting increases in motor function. Finally, the acute-TMS group showed increased fMRI-evoked responses to hindlimb stimulation over the right and left hindlimb (LHL) primary somatosensory representations (S1), respectively; the chronic-TMS group showed moderate sensory responses in comparison, and the no-TMS group exhibited the lowest sensory responses to both hindlimbs. Conclusion: The results suggest that rTMS therapy beginning in the acute phase after SCI promotes neuroplasticity and is an effective rehabilitative approach in a rat model of SCI.

Potential Application of Optogenetic Stimulation in the Treatment of Pain and Migraine Headache: A Perspective from Animal Studies

Optogenetic manipulation is uniquely useful in unraveling the functional organization of neuronal circuits in the central nervous system by enabling reversible gain- or loss-of-function of discrete populations of neurons within restricted brain regions. This state-of-the-art technology can produce circuit-specific neuromodulation by overexpressing light-sensitive proteins (opsins) in particular cell types of interest. Here, we discuss the principle of optogenetic manipulation and its application in pain research using animal models, and we also discuss how to potentially use optogenetic stimulation in the treatment of migraine headache in the future.

Selective photoactivation of neural activity combined with laser speckle imaging of cerebral blood flow

Neural activity leads to alterations in cerebral blood flow (CBF), i.e., neurovascular regulation, which is implicated in brain physiology and pathology. Here a method for simultaneous imaging of CBF and spatially selective photoactivation of neural activity is proposed. CBF was obtained by laser speckle contrast imaging, and a liquid-crystal spatial light modulator (LC-SLM) was used to generate photoactivation patterns targeting designated locations in the cortex. Animal experiments stimulating defined cortical regions of VGAT-ChR2 and wild-type mice were conducted, and experiments with low-intensity stimulation were performed to investigate the influence of background light produced by the LC-SLM.

Wireless control of cellular function by activation of a novel protein responsive to electromagnetic fields

The Kryptopterus bicirrhis (glass catfish) is known to respond to electromagnetic fields (EMF). Here we tested its avoidance behavior in response to static and alternating magnetic fields stimulation. Using expression cloning we identified an electromagnetic perceptive gene (EPG) from the K. bicirrhis encoding a protein that responds to EMF. This EPG gene was cloned and expressed in mammalian cells, neuronal cultures and in rat’s brain. Immunohistochemistry showed that the expression of EPG is confined to the mammalian cell membrane. Calcium imaging in mammalian cells and cultured neurons expressing EPG demonstrated that remote activation by EMF significantly increases intracellular calcium concentrations, indicative of cellular excitability. Moreover, wireless magnetic activation of EPG in rat motor cortex induced motor evoked responses of the contralateral forelimb in vivo. Here we report on the development of a new technology for remote, non-invasive modulation of cell function.

Altered microstructure rather than morphology in the corpus callosum after lower limb amputation

The corpus callosum (CC) has been implicated in the reorganization of the brain following amputation. However, it is unclear which regions of the CC are involved in this process. In this study, we explored the morphometric and microstructural changes in CC subregions in patients with unilateral lower limb amputation. Thirty-eight patients and 38 age- and gender-matched normal controls were included. The CC was divided into five regions, and the area, thickness and diffusion parameters of each region were investigated. While morphometric analysis showed no significant differences between the two groups, amputees showed significant higher values in axial diffusivity, radial diffusivity and mean diffusivity in region II of the CC, which connects the bilateral premotor and supplementary motor areas. In contrast, the mean fractional anisotropy value of the fibers generated by these cortical areas, as measured by tractography, was significantly smaller in amputees. These results demonstrate that the interhemispheric pathways contributing to motor coordination and imagery are reorganized in lower limb amputees.

Novel Neuromodulation Techniques to Assess Interhemispheric Communication in Neural Injury and Neurodegenerative Diseases

Interhemispheric interaction has a major role in various neurobehavioral functions. Its disruption is a major contributor to the pathological changes in the setting of brain injury such as traumatic brain injury, peripheral nerve injury, and stroke, as well as neurodegenerative diseases. Because interhemispheric interaction has a crucial role in functional consequence in these neuropathological states, a review of noninvasive and state-of-the-art molecular based neuromodulation methods that focus on or have the potential to elucidate interhemispheric interaction have been performed. This yielded approximately 170 relevant articles on human subjects or animal models. There has been a recent surge of reports on noninvasive methods such as transcranial magnetic stimulation and transcranial direct current stimulation. Since these are noninvasive techniques with little to no side effects, their widespread use in clinical studies can be easily justified. The overview of novel neuromodulation methods and how they can be applied to study the role of interhemispheric communication in neural injury and neurodegenerative disease is provided. Additionally, the potential of each method in therapeutic use as well as investigating the pathophysiology of interhemispheric interaction in neurodegenerative diseases and brain injury is discussed. New technologies such as transcranial magnetic stimulation or transcranial direct current stimulation could have a great impact in understanding interhemispheric pathophysiology associated with acquired injury and neurodegenerative diseases, as well as designing improved rehabilitation therapies. Also, advances in molecular based neuromodulation techniques such as optogenetics and other chemical, thermal, and magnetic based methods provide new capabilities to stimulate or inhibit a specific brain location and a specific neuronal population.

Layer-specific optogenetic activation of pyramidal neurons causes beta-gamma entrainment of neonatal networks

Coordinated activity patterns in the developing brain may contribute to the wiring of neuronal circuits underlying future behavioural requirements. However, causal evidence for this hypothesis has been difficult to obtain owing to the absence of tools for selective manipulation of oscillations during early development. We established a protocol that combines optogenetics with electrophysiological recordings from neonatal mice in vivo to elucidate the substrate of early network oscillations in the prefrontal cortex. We show that light-induced activation of layer II/III pyramidal neurons that are transfected by in utero electroporation with a high-efficiency channelrhodopsin drives frequency-specific spiking and boosts network oscillations within beta–gamma frequency range. By contrast, activation of layer V/VI pyramidal neurons causes nonspecific network activation. Thus, entrainment of neonatal prefrontal networks in fast rhythms relies on the activation of layer II/III pyramidal neurons. This approach used here may be useful for further interrogation of developing circuits, and their behavioural readout.

Oscillations in cortical activity during development are important for functional maturation. Here, the authors use optogenetics in neonatal mice to determine a causal role for pyramidal cell firing in different prelimbic cortex layers in generating beta–gamma range activity.

Role of Neuromodulation and Optogenetic Manipulation in Pain Treatment

Neuromodulation, including invasive and non-invasive stimulation, has been used to treat intractable chronic pain. However, the mechanisms by which neuromodulation produces antinociceptive effect still remain uncertain. Optogenetic manipulation, a recently developed novel approach, has already proven its value to clinicians by providing new insights into mechanisms of current clinical neuromodulation methods as well as pathophysiology of nervous system diseases at the circuit level. Here, we discuss the principles of two neuromodulation methods (deep brain stimulation and motor cortex stimulation) and their applications in pain treatment. More important, we summarize the new information from recent studies regarding optogenetic manipulation in neuroscience research and its potential utility in pain study.

Time to wake up: Studying neurovascular coupling and brain-wide circuit function in the un-anesthetized animal

Functional magnetic resonance imaging (fMRI) has allowed the noninvasive study of task-based and resting-state brain dynamics in humans by inferring neural activity from blood-oxygenation-level dependent (BOLD) signal changes. An accurate interpretation of the hemodynamic changes that underlie fMRI signals depends on the understanding of the quantitative relationship between changes in neural activity and changes in cerebral blood flow, oxygenation and volume. While there has been extensive study of neurovascular coupling in anesthetized animal models, anesthesia causes large disruptions of brain metabolism, neural responsiveness and cardiovascular function. Here, we review work showing that neurovascular coupling and brain circuit function in the awake animal are profoundly different from those in the anesthetized state. We argue that the time is right to study neurovascular coupling and brain circuit function in the awake animal to bridge the physiological mechanisms that underlie animal and human neuroimaging signals, and to interpret them in light of underlying neural mechanisms. Lastly, we discuss recent experimental innovations that have enabled the study of neurovascular coupling and brain-wide circuit function in un-anesthetized and behaving animal models.

The implications of injury in the developing nervous system on upper extremity function

STUDY DESIGN

Literature review.

PURPOSE

The corticospinal system (CS) and peripheral nervous system (PNS) are common sites of damage during the early stages of life. The prenatal or immediately prenatal period is the most common time for damage to occur. Here we briefly review the basic features of the development of the CS and the PNS and the clinical consequences of injury to or improper development of these systems on upper extremity (UE) function.

RESULTS

The proper development of both the CS and PNS is necessary to achieve adequate function of the (UE). Injury or improper development of these systems can lead to upper extremity dysfunction and limit participation in activities of daily living.

CONCLUSIONS

Both the PNS and CS play major roles in the proper functioning of the UE. A better understanding of their roles and common developmental disorders is needed to move rehabilitation of motor impairments forward.

Prospects for Optogenetic Augmentation of Brain Function

The ability to optically control neural activity opens up possibilities for the restoration of normal function following neurological disorders. The temporal precision, spatial resolution, and neuronal specificity that optogenetics offers is unequalled by other available methods, so will it be suitable for not only restoring but also extending brain function? As the first demonstrations of optically “implanted” novel memories emerge, we examine the suitability of optogenetics as a technique for extending neural function. While optogenetics is an effective tool for altering neural activity, the largest impediment for optogenetics in neural augmentation is our systems level understanding of brain function. Furthermore, a number of clinical limitations currently remain as substantial hurdles for the applications proposed. While neurotechnologies for treating brain disorders and interfacing with prosthetics have advanced rapidly in the past few years, partially addressing some of these critical problems, optogenetics is not yet suitable for use in humans. Instead we conclude that for the immediate future, optogenetics is the neurological equivalent of the 3D printer: its flexibility providing an ideal tool for testing and prototyping solutions for treating brain disorders and augmenting brain function.

Neuroplasticity for spontaneous functional recovery after neonatal hypoxic ischemic brain injury in rats observed by functional MRI and diffusion tensor imaging

For infants and children, an incredible resilience from injury is often observed. There is growing evidence that functional recovery after brain injury might well be a consequence of the reorganization of the neural network as a process of neuroplasticity. We demonstrate the presence of neuroplasticity at work in spontaneous recovery after neonatal hypoxic ischemic (HI) injury, by elucidating a precise picture in which such reorganization takes place using functional MRI techniques. For all 12 siblings, 6 rats were subjected to severe HI brain injury and 6 rats underwent sham operation only. Severe HI brain injury was induced to postnatal day 7 (p7) Sprague-Dawley rats according to the Rice-Vannucci model (right carotid artery occlusion followed by 150min of hypoxia with 8% O2 and 92% of N2). Brain activation maps along with anatomical and functional connectivity maps related to the sensory motor function were obtained at adult (p63) using blood oxygen level dependent (BOLD)-functional MRI (fMRI), resting state-functional MRI (rs-fMRI) and diffusion tensor imaging (DTI); each of these MRI data was related to sensory motor functional outcome. In-depth investigation of the functional MRI data revealed: 1) intra-hemispheric expansion of BOLD signal activation in the contralesional undamaged hemisphere for ipsilesional forepaw stimuli to include the M2 and Cg1 in addition to the S1 and M1 wide spreading in the anterior and posterior directions, 2) inter-hemispheric transfer of BOLD signal activation for contralesional forepaw stimuli, normally routed to the injured hemisphere, to analogous sites in the contralesional undamaged hemisphere, localized newly to the M1 and M2 with a reduced portion of the S1, 3) inter-hemispheric axonal disconnection and axonal rewiring within the undamaged hemisphere as shown through DTI, and 4) increased functional interactions within the cingulate gyrus in the HI injured rats as shown through rs-fMRI. The BOLD signal amplitudes as well as DTI and rs-fMRI data well correlate with behavioral tests (tape to remove). We found that function normally utilizing what would be the injured hemisphere is transferred to the uninjured hemisphere, and functionality of the uninjured hemisphere remains not untouched but is also rewired in an expansion corresponding to the newly formed sensorimotor function from both the contralesional and the ipsilesional sides. The conclusion drawn from the data in our current study is that enhanced motor function in the contralesional hemisphere governs both the normal and damaged sides, indicating that active plasticity with brain laterality was spontaneously generated to overcome functional loss and established autonomously through normal experience via modification of neural circuitry for neonatal HI injured brain.

Neural and hemodynamic responses to optogenetic and sensory stimulation in the rat somatosensory cortex

Introducing optogenetics into neurovascular research can provide novel insights into the cell-specific control of the hemodynamic response. To generalize findings from molecular approaches, it is crucial to determine whether light-activated circuits have the same effect on the vasculature as sensory-activated ones. For that purpose, rats expressing channelrhodopsin (ChR2) specific to excitatory glutamatergic neurons were used to measure neural activity, blood flow, hemoglobin-based optical intrinsic signal, and blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) during optogenetic and sensory stimulation. The magnitude of the evoked hemodynamic responses was monotonically correlated with optogenetic stimulus strength. The BOLD hemodynamic response function was consistent for optogenetic and sensory stimuli. The relationship between electrical activities and hemodynamic responses was comparable for optogenetic and sensory stimuli, and better explained by the local field potential (LFP) than the firing rate. The LFP was well correlated with cerebral blood flow, moderately with cerebral blood volume, and less with deoxyhemoglobin (dHb) level. The presynaptic firing rate had little impact on evoking vascular response. Contribution of the postsynaptic LFP to the blood flow response induced by optogenetic stimulus was further confirmed by the application of glutamate receptor antagonists. Overall, neurovascular coupling during optogenetic control of glutamatergic neurons largely conforms to that of a sensory stimulus.

Mapping the functional network of medial prefrontal cortex by combining optogenetics and fMRI in awake rats

The medial prefrontal cortex (mPFC) plays a critical role in multiple cognitive and limbic functions. Given its vital importance, investigating the function of individual mPFC circuits in animal models has provided critical insight into the neural basis underlying different behaviors and psychiatric conditions. However, our knowledge regarding the mPFC whole-brain network stays largely at the anatomical level, while the functional network of mPFC, which can be dynamic in different conditions or following manipulations, remains elusive especially in awake rodents. Here we combined optogenetic stimulation and functional magnetic resonance imaging (opto-fMRI) to reveal the network of brain regions functionally activated by mPFC outputs in awake rodents. Our data showed significant increases in blood-oxygenation-level dependent (BOLD) signals in prefrontal, striatal and limbic regions when mPFC was optically stimulated. This activation pattern was robust, reproducible, and did not depend on the stimulation period in awake rats. BOLD signals, however, were substantially reduced when animals were anesthetized. In addition, regional brain activation showing increased BOLD signals during mPFC stimulation was corroborated by electrophysiological recordings. These results expand the applicability of the opto-fMRI approach from sensorimotor processing to cognition-related networks in awake rodents. Importantly, it may help elucidate the circuit mechanisms underlying numerous mPFC-related functions and behaviors that need to be assessed in the awake state.

Normalized activation in the somatosensory cortex 30 years following nerve repair in children: an fMRI study

The clinical outcome following a peripheral nerve injury in the upper extremity is generally better in young children than in teenagers and in adults, but the mechanism behind this difference is unknown. In 28 patients with a complete median nerve injury sustained at the ages of 1-13 years (n = 13) and 14-20 years (n = 15), the cortical activation during tactile finger stimulation of the injured and healthy hands was monitored at a median time since injury of 28 years using functional magnetic resonance imaging (fMRI) at 3 Tesla. The results from the fMRI were compared with the clinical outcome and electroneurography. The cortical activation pattern following sensory stimulation of the median nerve-innervated fingers was dependent on the patient's age at injury. Those injured at a young age (1-13 years) had an activation pattern similar to that of healthy controls. Furthermore, they showed a clinical outcome significantly superior (P = 0.001) to the outcome in subjects injured at a later age; however, electroneurographical parameters did not differ between the groups. In subjects injured at age 14-20 years, a more extended activation of the contralateral hemisphere was seen in general. Interestingly, these patients also displayed changes in the ipsilateral hemisphere where a reduced inhibition of somatosensory areas was seen. This loss of ipsilateral inhibition correlated to increasing age at injury as well as to poor recovery of sensory functions in the hand. In conclusion, cerebral changes in both brain hemispheres may explain differences in clinical outcome following a median nerve injury in childhood or adolescence.

Increased cortical responses to forepaw stimuli immediately after peripheral deafferentation of hindpaw inputs

Both central and peripheral injuries of the nervous system induce dramatic reorganization of the primary somatosensory cortex. We recently showed that spinal cord injuries at thoracic level in anesthetized rats can immediately increase the responses evoked in the forepaw cortex by forepaw stimuli (above the level of the lesion), suggesting that the immediate cortical reorganization after deafferentation can extend across cortical representations of different paws. Here we show that a complete deafferentation of inputs from the hindpaw induced by injury or pharmacological block of the peripheral nerves in anesthetized rats also increases the responses evoked in the forepaw cortex by forepaw stimuli. This increase of cortical responses after peripheral deafferentation is not associated with gross alterations in the state of cortical spontaneous activity. The results of the present study, together with our previous works on spinal cord injury, suggest that the forepaw somatosensory cortex is critically involved in the reorganization that starts immediately after central or peripheral deafferentation of hindpaw inputs.

Peripheral nerve reconstruction after injury: a review of clinical and experimental therapies

Unlike other tissues in the body, peripheral nerve regeneration is slow and usually incomplete. Less than half of patients who undergo nerve repair after injury regain good to excellent motor or sensory function and current surgical techniques are similar to those described by Sunderland more than 60 years ago. Our increasing knowledge about nerve physiology and regeneration far outweighs our surgical abilities to reconstruct damaged nerves and successfully regenerate motor and sensory function. It is technically possible to reconstruct nerves at the fascicular level but not at the level of individual axons. Recent surgical options including nerve transfers demonstrate promise in improving outcomes for proximal nerve injuries and experimental molecular and bioengineering strategies are being developed to overcome biological roadblocks limiting patient recovery.

Peripheral nerve reconstruction after injury: a review of clinical and experimental therapies

Unlike other tissues in the body, peripheral nerve regeneration is slow and usually incomplete. Less than half of patients who undergo nerve repair after injury regain good to excellent motor or sensory function and current surgical techniques are similar to those described by Sunderland more than 60 years ago. Our increasing knowledge about nerve physiology and regeneration far outweighs our surgical abilities to reconstruct damaged nerves and successfully regenerate motor and sensory function. It is technically possible to reconstruct nerves at the fascicular level but not at the level of individual axons. Recent surgical options including nerve transfers demonstrate promise in improving outcomes for proximal nerve injuries and experimental molecular and bioengineering strategies are being developed to overcome biological roadblocks limiting patient recovery.

Optogenetic neuronal stimulation promotes functional recovery after stroke

Clinical and research efforts have focused on promoting functional recovery after stroke. Brain stimulation strategies are particularly promising because they allow direct manipulation of the target area's excitability. However, elucidating the cell type and mechanisms mediating recovery has been difficult because existing stimulation techniques nonspecifically target all cell types near the stimulated site. To circumvent these barriers, we used optogenetics to selectively activate neurons that express channelrhodopsin 2 and demonstrated that selective neuronal stimulations in the ipsilesional primary motor cortex (iM1) can promote functional recovery. Stroke mice that received repeated neuronal stimulations exhibited significant improvement in cerebral blood flow and the neurovascular coupling response, as well as increased expression of activity-dependent neurotrophins in the contralesional cortex, including brain-derived neurotrophic factor, nerve growth factor, and neurotrophin 3. Western analysis also indicated that stimulated mice exhibited a significant increase in the expression of a plasticity marker growth-associated protein 43. Moreover, iM1 neuronal stimulations promoted functional recovery, as stimulated stroke mice showed faster weight gain and performed significantly better in sensory-motor behavior tests. Interestingly, stimulations in normal nonstroke mice did not alter motor behavior or neurotrophin expression, suggesting that the prorecovery effect of selective neuronal stimulations is dependent on the poststroke environment. These results demonstrate that stimulation of neurons in the stroke hemisphere is sufficient to promote recovery.

Molecular neuroimaging of post-injury plasticity

Nerve injury induces long-term changes in neuronal activity in the primary somatosensory cortex (S1), which has often been implicated as the origin of sensory dysfunction. However, the cellular mechanisms underlying this phenomenon remain unclear. C-fos is an immediate early gene, which has been shown to play an instrumental role in plasticity. By developing a new platform to image real-time changes in gene expression in vivo, we investigated whether injury modulates the levels of c-fos in layer V of S1, since previous studies have suggested that these neurons are particularly susceptible to injury. The yellow fluorescent protein, ZsYellow1, under the regulation of the c-fos promoter, was expressed throughout the rat brain. A fiber-based confocal microscope that enabled deep brain imaging was utilized, and local field potentials were collected simultaneously. In the weeks following limb denervation in adult rats (n=10), sensory stimulation of the intact limb induced significant increases in c-fos gene expression in cells located in S1, both contralateral (affected, 27.6±3 cells) and ipsilateral (8.6±3 cells) to the injury, compared to controls (n=10, 13.4±3 and 1.0±1, respectively, p value<0.05). Thus, we demonstrated that injury activates cellular mechanisms that are involved in reshaping neuronal connections, and this may translate to neurorehabilitative potential.

Study of the spatial correlation between neuronal activity and BOLD fMRI responses evoked by sensory and channelrhodopsin-2 stimulation in the rat somatosensory cortex

In this work, we combined optogenetic tools with high-resolution blood oxygenation level-dependent functional MRI (BOLD fMRI), electrophysiology, and optical imaging of cerebral blood flow (CBF), to study the spatial correlation between the hemodynamic responses and neuronal activity. We first investigated the spatial and temporal characteristics of BOLD fMRI and the underlying neuronal responses evoked by sensory stimulations at different frequencies. The results demonstrated that under dexmedetomidine anesthesia, BOLD fMRI and neuronal activity in the rat primary somatosensory cortex (S1) have different frequency-dependency and distinct laminar activation profiles. We then found that localized activation of channelrhodopsin-2 (ChR2) expressed in neurons throughout the cortex induced neuronal responses that were confined to the light stimulation S1 region (<500 μm) with distinct laminar activation profile. However, the spatial extent of the hemodynamic responses measured by CBF and BOLD fMRI induced by both ChR2 and sensory stimulation was greater than 3 mm. These results suggest that due to the complex neurovascular coupling, it is challenging to determine specific characteristics of the underlying neuronal activity exclusively from the BOLD fMRI signals.

Evidence for impaired plasticity after traumatic brain injury in the developing brain

The robustness of plasticity mechanisms during brain development is essential for synaptic formation and has a beneficial outcome after sensory deprivation. However, the role of plasticity in recovery after acute brain injury in children has not been well defined. Traumatic brain injury (TBI) is the leading cause of death and disability among children, and long-term disability from pediatric TBI can be particularly devastating. We investigated the altered cortical plasticity 2-3 weeks after injury in a pediatric rat model of TBI. Significant decreases in neurophysiological responses across the depth of the noninjured, primary somatosensory cortex (S1) in TBI rats, compared to age-matched controls, were detected with electrophysiological measurements of multi-unit activity (86.4% decrease), local field potential (75.3% decrease), and functional magnetic resonance imaging (77.6% decrease). Because the corpus callosum is a clinically important white matter tract that was shown to be consistently involved in post-traumatic axonal injury, we investigated its anatomical and functional characteristics after TBI. Indeed, corpus callosum abnormalities in TBI rats were detected with diffusion tensor imaging (9.3% decrease in fractional anisotropy) and histopathological analysis (14% myelination volume decreases). Whole-cell patch clamp recordings further revealed that TBI results in significant decreases in spontaneous firing rate (57% decrease) and the potential to induce long-term potentiation in neurons located in layer V of the noninjured S1 by stimulation of the corpus callosum (82% decrease). The results suggest that post-TBI plasticity can translate into inappropriate neuronal connections and dramatic changes in the function of neuronal networks.

Optical developments for optogenetics

Brain intricacies and the difficulty that scientists encounter in revealing its function with standard approaches such as electrical stimulation of neurons have led to the exploration of new tools that enable the study of neural circuits in a remote and non-invasive way. To this end, optogenetics has initialised a revolution for neuroscience in the last decade by enabling simultaneous monitoring and stimulation of specific neuronal populations in intact brain preparations through genetically targeted expression of light sensitive proteins and molecular photoswitches. In addition to ongoing molecular probe development and optimisation, novel optical techniques hold immense potential to amplify and diversify the utility of optogenetic methods. Importantly, by improving the spatio-temporal resolution of light stimulation, neural circuits can be photoactivated in patterns mimicking endogenous physiological processes. The following synopsis addresses the possibilities and limitations of optical stimulation methods applied to and developed for activation of neuronal optogenetic tools.

Genetic tools to manipulate MRI contrast

Advances in molecular biology in the early 1970s revolutionized research strategies for the study of complex biological processes, which, in turn, created a high demand for new means to visualize these dynamic biological changes noninvasively and in real time. In this respect, MRI was a perfect fit, because of the versatile possibility to alter the different contrast mechanisms. Genetic manipulations are now being translated to MRI through the development of reporters and sensors, as well as the imaging of transgenic and knockout mice. In the past few years, a new molecular biology toolset, namely optogenetics, has emerged, which allows for the manipulation of cellular behavior using light. This technology provides a few particularly attractive features for combination with newly developed MRI techniques for the probing of in vivo cellular and, in particular, neural processes, specifically the ability to control focal, genetically defined cellular populations with high temporal resolution using equipment that is magnetically inert and does not interact with radiofrequency pulses. Recent studies have demonstrated that the combination of optogenetics and functional MRI (fMRI) can provide an appropriate platform to investigate in vivo, at the cellular and molecular levels, the neuronal basis of fMRI signals. In addition, this novel combination of optogenetics with fMRI has the potential to resolve pre-synaptic versus post-synaptic changes in neuronal activity and changes in the activity of large neuronal networks in the context of plasticity associated with development, learning and pathophysiology.

Neurovascular coupling: in vivo optical techniques for functional brain imaging

Optical imaging techniques reflect different biochemical processes in the brain, which is closely related with neural activity. Scientists and clinicians employ a variety of optical imaging technologies to visualize and study the relationship between neurons, glial cells and blood vessels. In this paper, we present an overview of the current optical approaches used for the in vivo imaging of neurovascular coupling events in small animal models. These techniques include 2-photon microscopy, laser speckle contrast imaging (LSCI), voltage-sensitive dye imaging (VSDi), functional photoacoustic microscopy (fPAM), functional near-infrared spectroscopy imaging (fNIRS) and multimodal imaging techniques. The basic principles of each technique are described in detail, followed by examples of current applications from cutting-edge studies of cerebral neurovascular coupling functions and metabolic. Moreover, we provide a glimpse of the possible ways in which these techniques might be translated to human studies for clinical investigations of pathophysiology and disease. In vivo optical imaging techniques continue to expand and evolve, allowing us to discover fundamental basis of neurovascular coupling roles in cerebral physiology and pathophysiology.

Peripheral nerve injury induces immediate increases in layer v neuronal activity

BACKGROUND

Peripheral nerve injury leads to changes in neuronal activity in the contralateral and ipsilateral primary somatosensory cortices (S1), which may lead to enduring sensory dysfunction and pain. Plasticity in the barrel and visual cortices has been shown to occur in a layer-specific manner. However, little is known about the layer specific changes associated with limb injury.

OBJECTIVE

To determine the layer-specific changes in neuronal activity associated with short-term plasticity induced by peripheral nerve injury in the rat.

METHODS

In vivo electrophysiology recordings (multiunit activity and local field potential) and high-resolution functional magnetic resonance imaging techniques were applied to characterize neuronal and hemodynamic responses across the depth of S1 contralateral and ipsilateral to the injury.

RESULTS

Within 60 minutes following injury, atypical increases in neuronal and hemodynamic responses in the deprived S1, ipsilateral to the noninjured limb, were observed in response to stimulation of the noninjured limb. The most prominent increases in neuronal activity in the deprived S1 occurred in layer V.

CONCLUSION

Layer V neurons provide the major output of S1 and they send and receive transcallosal input. Thus, the immediate changes in neuronal firing patterns in layer V induced by the injury, can adversely affect the activity of subcortical regions and also interfere with normal cortical processing and interhemispheric communication. Therefore, a rehabilitation strategy that targets layer V neurons activity and starts immediately after the injury may benefit the functional outcome.

Laser Speckle Contrast Imaging: theory, instrumentation and applications

Laser Speckle Contrast Imaging (LSCI) is a wide field of view, non scanning optical technique for observing blood flow. Speckles are produced when coherent light scattered back from biological tissue is diffracted through the limiting aperture of focusing optics. Mobile scatterers cause the speckle pattern to blur; a model can be constructed by inversely relating the degree of blur, termed speckle contrast to the scatterer speed. In tissue, red blood cells are the main source of moving scatterers. Therefore, blood flow acts as a virtual contrast agent, outlining blood vessels. The spatial resolution (~10 μm) and temporal resolution (10 ms to 10 s) of LSCI can be tailored to the application. Restricted by the penetration depth of light, LSCI can only visualize superficial blood flow. Additionally, due to its non scanning nature, LSCI is unable to provide depth resolved images. The simple setup and non-dependence on exogenous contrast agents have made LSCI a popular tool for studying vascular structure and blood flow dynamics. We discuss the theory and practice of LSCI and critically analyze its merit in major areas of application such as retinal imaging, imaging of skin perfusion as well as imaging of neurophysiology.

Optogenetic insights into social behavior function

Cognitive and social deficits lie at the core of many neuropsychiatric diseases and are among the many behavioral symptoms not amenable to pharmacological intervention. Despite significant advances in identifying genes potentially involved in the pathogenesis of complex psychiatric conditions such as autism and schizophrenia, knowledge of the physiological functions that are affected (and are therefore potential targets for clinical intervention) is scarce. In psychiatric disorders with a strong genetic component, animal models have provided important links between disease-related genes and behavioral impairment. Social dysfunction, for instance, is commonly observed in transgenic rodent disease models. However, the causal relationships between the behavioral and physiological abnormalities in these models are not well-understood. Optogenetic techniques have evolved to provide a wide range of experimental paradigms in which neural circuit activity can be perturbed with high spatial and temporal precision, enabling causal investigation of the function of defined physiological events in neuronal subgroups. With optogenetics, researchers have begun to elucidate the basic neural mechanisms of social behaviors and of disease-relevant social and cognitive dysfunction. The synthesis of optogenetic technology with genetic animal models will allow forward- and reverse-engineering approaches to investigating the neural correlates of psychiatric disease. This review outlines the neural systems known to be involved in social behavior, illustrates how optogenetic technology has been applied to analyze this circuitry, and imagines how it might be further developed in future studies to elucidate these complex circuits both from a basic science perspective and in the context of psychiatric disease.

Columnar specificity of microvascular oxygenation and blood flow response in primary visual cortex: evaluation by local field potential and spiking activity

The relation of cortical microcirculation, oxygen metabolism, and underlying neuronal network activity remains poorly understood. Anatomical distribution of cortical microvasculature and its relationship to cortical functional domains suggests that functional organizations may be revealed by mapping cerebral blood flow responses. However, there is little direct experimental evidence and a lack of electrophysiological evaluation. In this study, we mapped ocular-dominance columns in primary visual cortex (V1) of anesthetized macaques with capillary flow-based laser speckle contrast imaging and deoxyhemoglobin-based intrinsic optical imaging. In parallel, the local field potentials (LFPs) and spikes were recorded from a linear array of eight microelectrodes, carefully positioned into left and right eye columns in V1. We found differential activation maps of blood flow, after masking large superficial draining vessels, exhibited a column-like pattern similar as the oximetric maps. Both the activated spikes and γ-band LFP demonstrated corresponding eye preference, consistent with the imaging maps. Our results present direct support in favor of previous proposals that the regulation of microcirculation can be as fine as the submillimeter scale, suggesting that cortical vasculature is functionally organized at the columnar level in a manner appropriate for supplying energy demands of functionally specific neuronal populations.