We thank Dr Dan Green for providing technical input during the development of these experimental techniques. This work was supported by NIH Grant R01-EY016849A and the Smith Family New Investigator Award.

Part I: Fabrication of Tungsten-in-Glass Electrodes
<ol>
 <li>A graphite ring is placed in a beaker filled with a concentrated solution of sodium nitrate (0.71g/mL) and potassium hydroxide (0.34g/mL) dissolved in water1, and the beaker is placed under the sewing arm of a modified sewing machine. </li>
 <li>Tungsten wire (0.5mm diameter, 6cm length) is taped to the sewing arm so that it is partially immersed (1-2cm) in solution. </li>
 <li>2V are applied across the tungsten wire by attaching a positive lead to the sewing arm and a negative lead to the graphite ring. </li>
 <li>The sewing machine is turned on and the tungsten wire is dipped repetitively into solution at a rate of ~4Hz for 2 min, which electrolytically etches the metal to a sharp point. </li>
 <li>The etched wire is placed on a manual micromanipulator and the point aligned under microscopic guidance (40x magnification) with the shaft of a glass pipette (0.25mm OD, 0.175mm ID) pulled to a 1mm tip with a glass puller. To prevent movement during wire insertion, the glass is temporarily secured to the microscope stage with putty.</li>
 <li>The wire is carefully advanced into the unpulled end of the glass, down the shaft, and through the 1&mu;m opening A small piece of glass is seen to break off the tip in the video, indicating a tight fit of the tungsten in the glass. The wire should extend around 5-10mm beyond the tip for rat optic fiber recordings.</li>
 <li>Cyanoacrylate is applied to the unpulled end of the glass and after hardening the electrical impedance is measured, where 1M&Omega; electrodes generally work best.</li>
</ol>
Part II: Stereotaxic Setup and Spike Train Recordings
<ol>
 <li>The stimulus display system is illustrated in the video, along with the stereotaxic apparatus and microdrive for positioning and lowering the electrode into the brain.</li>
 <li>To perform retinal spike train recordings the rat is anesthetized and later paralyzed. Standard procedures (not illustrated) are used for surgical insertion of a femoral vein cannula for drug delivery and a tracheal (Y-tube) cannula for mechanical ventilation during paralysis. The experiments are terminal for the animal. </li>
 <li>After preparatory procedures, the animal is placed on the heating blanket and the head is fixed into stereotaxic position, as defined by rat brain atlas2, with ear and tooth bars. </li>
 <li>The rectal probe is inserted, which controls the heating blanket via a homeothermic control unit that maintains body temperature at 37&deg;C.</li>
 <li>Metal needle are used as leads to measure the electrocardiogram and monitor heart rate. </li>
 <li>The skin is opened on top of the skull and the intersection of skull plates (bregma) is exposed. A custom-designed crossbar frame is set in place, a circle is marked on the skull around begma through a hole in the crossbar, and the crossbar is temporarily removed.</li>
 <li>The stereotaxic system is calibrated by positioning the guide needle over bregma. A 5-mm hole is drilled into the skull at the marked location and the bone is removed, exposing the brain. A thin ring of putty is placed around the opening in the skull to form a seal around the hole in the crossbar, which is reset into place. </li>
 <li>If the animal has been at a stable plane of anesthesia for awhile, it is injected with paralytic in order to prevent eye movements during data collection. After breathing stops the animal is mechanically ventilated. A custom program tracks ventilation and physiological parameters throughout the experiment and informs the experimenter if compensatory action is needed should any parameters go outside normal levels.</li>
 <li>The guide needle is backloaded with the tungsten electrode and lowered into the brain. After brain penetration the crossbar hole is filled with agar (not shown), and the microdrive assembly is clamped to the crossbar for mechanical stability. The tungsten electrode is then slowly advanced (2&mu;m/sec) out the guide needle until the tip is about 8-9mm below the skull, where the optic chiasm is located.</li>
 <li>Spike trains belonging to retinal ganglion cells are identified by their response to visual input. Upon isolation of a single optic fiber the receptive field of the recorded cell is mapped in visual space and its response properties are characterized with drifting gratings or other visual patterns of interest. The stability of the system allows for single-unit recordings of several hours3.</li>
</ol>
Materials
Adult Brown-Norway rats (250-400g) were purchased from a commercial vendor and housed under a regulated (12/12) light/dark cycle. Anesthesia was induced with an intraperitoneal injection of ketamine hydrochloride and xylazine (70 and 2 mg/kg, respectively, Henry Schein Inc) and maintained for the duration of the experiment with an intravenous infusion of ketamine and xylazine (30 and 1 mg/kg/hr) mixed with dextrose, saline, and gallamine triethiodide (40 mg/kg/hr, Fischer Inc) through a catheter (0.13mm OD, Small Parts Inc) in the right femoral vein. Gallamine is included in the mixture to paralyze eye movements. The infusion rate of the pump (WPI Inc) was adjusted as needed to maintain a stable plane of anesthesia as assessed by heart rate and blood pressure variability. After paralysis, the animal was mechanically ventilated (Harvard Apparatus, Model 683) through a tracheal cannula at 60-80 breaths/min (2cc volume), with the rate adjusted as necessary to maintain end-tidal CO2 measured with an in-line capnometer (Novametrix Inc, Model 710Sp) at 30%. Body temperature was regulated via a homeothermic blanket control system (Harvard Apparatus Inc). Body temperature, end-tidal CO2, heart rate, and blood pressure were continuously monitored throughout the experiment by a LABVIEW program. Visual stimuli were presented on a Sony Multiscan 17e CRT monitor (mean luminance of 30 cd/m2) running at 100 Hz with a resolution of 800x600 pixels. Data acquisition and monitor output were controlled with custom software written in Matlab and LabView in conjunction with a video image processor (Cambridge Research Systems Inc, Bits++) and the Psychophysics Toolbox4. The animal viewed the stimulus display (40.4 x 30.2 cm) at a distance of 16.5cm through contact lenses (Ocular Instruments Inc), and ophthalmic solution was applied periodically during the experiment to keep the eyes moist. The visual field accessible to stimulation was maximized by reverse mounting the animal in a stereotaxic apparatus (Stoelting Co) elevated 14cm above the surface of a floating table (TMC Inc) and setting the monitor on a custom-designed sled that moved on the table along a &plusmn;100 deg arc about the nose. This provided a repositionable display field that extended 60-deg above and 35-deg below eye level and &plusmn;42-deg laterally from the center of monitor. Tungsten electodes were fabricated with wire obtained from Small Parts Inc and custom borosilicate glass obtained from Friedrich and Dimmock Inc. A standard micropippete puller (Sutter Instruments, Model P-97) was used to shape the glass tip. The electrode impedance tester was purchased from Bak-Electronics. Electrodes were advanced with a motorized microdrive system (Newport Inc, StepperMike). Electrocardiogram and optic nerve signals were amplified and filtered with a high input impedance multielectrode amplifier (FHC Inc, X-Cell 3x4). Heart beats were detected with a window discriminator (WPI Inc, Model 121). Nerve action potentials were detected and time stamped with 0.1ms resolution by a digital spike discriminator (FHC Inc, APM). The spike discriminator was gated by a trigger signal from the video image processor so that spike times were locked to the stimulus.

<ol>
	<li>Levick, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Another+tungsten+microelectrode.">Another tungsten microelectrode.</a> Med Biol Eng. 10 (4), 510-515 (1972).</li><li>Paxinos, G., Watson, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The rat brain in stereotaxic coordinates. , (1998).</li><li>Freeman, D. K., Heine, W. F., Passaglia, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+maintained+discharge+of+rat+retinal+ganglion+cells.">The maintained discharge of rat retinal ganglion cells.</a> Vis Neurosci. 25 (4), 535-548 (2008).</li><li>Brainard, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+psychophysics+toolbox.">The psychophysics toolbox.</a> Spat Vis. 10, 433-436 (1997).</li></ol>

All experimental procedures were approved by the Institutional Animal Care and Use Committee at Boston University.

Optic fiber recordings are an attractive approach for addressing experimental questions about retinal information encoding and transmission that require an intact eye. Moreover, the signaling properties of both eyes can be studied in virtually the same physiological state if the electrode is positioned in the optic chiasm or tract where the activity of crossed and uncrossed optic nerve fibers can be recorded with a single electrode penetration. Optic fiber recordings are common in cat but not in other popular animals mod...

single-unit in vivo recordings from the optic chiasm of rat

Information about the visual world is transmitted to the brain in sequences of action potentials in retinal ganglion cell axons that make up the optic nerve. In vivo recordings of ganglion cell spike trains in several animal models have revealed much of what is known about how the early visual system processes and encodes visual information. However, such recordings have been rare in one of the most common animal models, the rat, possibly owing to difficulty in detecting spikes fired by small diameter axons. The many retinal disease models involving rats motivate a need for characterizing the functional properties of ganglion cells without disturbing the eye, as with intraocular or in vitro recordings. Here, we demonstrate a method for recording ganglion cell spike trains from the optic chiasm of the anesthetized rat. We first show how to fabricate tungsten-in-glass electrodes that can pick up electrical activity from single ganglion cell axons in rat. The electrodes outperform all commercial ones that we have tried. We then illustrate our custom-designed stereotaxic system for in vivo visual neurophysiology experiments and our procedures for animal preparation and reliable and stable electrode placement in the optic chiasm.

Watch this Scientific Journal Video about Single-unit In vivo Recordings from the Optic Chiasm of Rat at JoVE.com

Single-unit In vivo Recordings from the Optic Chiasm of Rat

Retinal ganglion cells transmit visual information from the eye to the brain with sequences of action potentials. Here, we demonstrate how to record the action potentials of single ganglion cells in vivo from anesthetized rats.

Single-unit In vivo Recordings from the Optic Chiasm of Rat

Information about the visual world is transmitted to the brain in sequences of action potentials in retinal ganglion cell axons that make up the optic ...

single-unit-in-vivo-recordings-from-the-optic-chiasm-of-rat

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Neuroscience

11.6K Views.  Boston University. Retinal ganglion cells transmit visual information from the eye to the brain with sequences of action potentials. Here, we demonstrate how to record the action potentials of single ganglion cells in vivo from anesthetized rats.

Video: Single-unit In vivo Recordings from the Optic Chiasm of Rat

Retrograde Fluorescent Labeling Allows for Targeted Extracellular Single-unit Recording from Identified Neurons In vivo

The overall goal of this method is to record single-unit responses from an identified population of neurons. In vivo electrophysiological recordings from individual neurons are critical for understanding how neural circuits function under natural conditions. Traditionally, these recordings have been performed 'blind', meaning the identity of the recorded cell is unknown at the start of the recording. Cellular identity can be subsequently determined via intracellular1, juxtacellular2 or loose-patch3 iontophoresis of dye, but these recordings cannot be pre-targeted to specific neurons in regions with functionally heterogeneous cell types. Fluorescent proteins can be expressed in a cell-type specific manner permitting visually-guided single-cell electrophysiology4-6. However, there are many model systems for which these genetic tools are not available. Even in genetically accessible model systems, the desired promoter may be unknown or genetically homogenous neurons may have varying projection patterns. Similarly, viral vectors have been used to label specific subgroups of projection neurons7, but use of this method is limited by toxicity and lack of trans-synaptic specificity. Thus, additional techniques that offer specific pre-visualization to record from identified single neurons in vivo are needed. Pre-visualization of the target neuron is particularly useful for challenging recording conditions, for which classical single-cell recordings are often prohibitively difficult8-11. The novel technique described in this paper uses retrograde transport of a fluorescent dye applied using tungsten needles to rapidly and selectively label a specific subset of cells within a particular brain region based on their unique axonal projections, thereby providing a visual cue to obtain targeted electrophysiological recordings from identified neurons in an intact circuit within a vertebrate CNS.
The most significant novel advancement of our method is the use of fluorescent labeling to target specific cell types in a non-genetically accessible model system. Weakly electric fish are an excellent model system for studying neural circuits in awake, behaving animals12. We utilized this technique to study sensory processing by "small cells" in the anterior exterolateral nucleus (ELa) of weakly electric mormyrid fish. "Small cells" are hypothesized to be time comparator neurons important for detecting submillisecond differences in the arrival times of presynaptic spikes13. However, anatomical features such as dense myelin, engulfing synapses, and small cell bodies have made it extremely difficult to record from these cells using traditional methods11, 14. Here we demonstrate that our novel method selectively labels these cells in 28% of preparations, allowing for reliable, robust recordings and characterization of responses to electrosensory stimulation.

Retrograde Fluorescent Labeling Allows for Targeted Extracellular Single-unit Recording from Identified Neurons In vivo

Retrograde transport of fluorescent dye labels a sub-population of neurons based on anatomical projection. Labeled axons can be visually targeted in vivo, permitting extracellular recording from identified axons. This technique facilitates recording when neurons cannot be labeled through genetic manipulation or are difficult to isolate using 'blind' in vivo approaches.

The overall goal of this method is to record single-unit responses from an identified population of neurons. In vivo electrophysiological recordings from ...

A Procedure for Implanting Organized Arrays of Microwires for Single-unit Recordings in Awake, Behaving Animals

In vivo electrophysiological recordings in the awake, behaving animal provide a powerful method for understanding neural signaling at the single-cell level. The technique allows experimenters to examine temporally and regionally specific firing patterns in order to correlate recorded action potentials with ongoing behavior. Moreover, single-unit recordings can be combined with a plethora of other techniques in order to produce comprehensive explanations of neural function. In this article, we describe the anesthesia and preparation for microwire implantation. Subsequently, we enumerate the necessary equipment and surgical steps to accurately insert a microwire array into a target structure. Lastly, we briefly describe the equipment used to record from each individual electrode in the array. The fixed microwire arrays described are well-suited for chronic implantation and allow for longitudinal recordings of neural data in almost any behavioral preparation. We discuss tracing electrode tracks to triangulate microwire positions as well as ways to combine microwire implantation with immunohistochemical techniques in order to increase the anatomical specificity of recorded results.

Implanting organized arrays of microwires for use in single-unit electrophysiological recordings presents a number of technical challenges.&#160;Methods for performing this technique and the equipment necessary are described.&#160;Also, the beneficial use of organized microwire arrays to record from distinct neural subregions with high spatial selectivity is discussed.

In vivo electrophysiological recordings in the awake, behaving animal provide a powerful method for understanding neural signaling at the single-cell ...

In vivo Imaging of Optic Nerve Fiber Integrity by Contrast-Enhanced MRI in Mice

The rodent visual system encompasses retinal ganglion cells and their axons that form the optic nerve to enter thalamic and midbrain centers, and postsynaptic projections to the visual cortex. Based on its distinct anatomical structure and convenient accessibility, it has become the favored structure for studies on neuronal survival, axonal regeneration, and synaptic plasticity. Recent advancements in MR imaging have enabled the in vivo visualization of the retino-tectal part of this projection using manganese mediated contrast enhancement (MEMRI). Here, we present a MEMRI protocol for illustration of the visual projection in mice, by which resolutions of (200 &#181;m)3 can be achieved using common 3 Tesla scanners. We demonstrate how intravitreal injection of a single dosage of 15 nmol MnCl2 leads to a saturated enhancement of the intact projection within 24 hr. With exception of the retina, changes in signal intensity are independent of coincided visual stimulation or physiological aging. We further apply this technique to longitudinally monitor axonal degeneration in response to acute optic nerve injury, a paradigm by which Mn2+ transport completely arrests at the lesion site. Conversely, active Mn2+ transport is quantitatively proportionate to the viability, number, and electrical activity of axon fibers. For such an analysis, we exemplify Mn2+ transport kinetics along the visual path in a transgenic mouse model (NF-&#954;B p50KO) displaying spontaneous atrophy of sensory, including visual, projections. In these mice, MEMRI indicates reduced but not delayed Mn2+ transport as compared to wild type mice, thus revealing signs of structural and/or functional impairments by NF-&#954;B mutations.
In summary, MEMRI conveniently bridges in vivo assays and post mortem histology for the characterization of nerve fiber integrity and activity. It is highly useful for longitudinal studies on axonal degeneration and regeneration, and investigations of mutant mice for genuine or inducible phenotypes.

In vivo Imaging of Optic Nerve Fiber Integrity by Contrast-Enhanced MRI in Mice

This video illustrates a method, using a clinical 3 T scanner, for contrast-enhanced MR imaging of the na&#239;ve mouse visual projection and for repetitive and longitudinal in vivo studies of optic nerve degeneration associated with acute optic nerve crush injury and chronic optic nerve degeneration in knock-out mice (p50KO).

The rodent visual system encompasses retinal ganglion cells and their axons that form the optic nerve to enter thalamic and midbrain centers, and ...

A Guide to In vivo Single-unit Recording from Optogenetically Identified Cortical Inhibitory Interneurons

A major challenge in neurophysiology has been to characterize the response properties and function of the numerous inhibitory cell types in the cerebral cortex. We here share our strategy for obtaining stable, well-isolated single-unit recordings from identified inhibitory interneurons in the anesthetized mouse cortex using a method developed by Lima and colleagues1. Recordings are performed in mice expressing Channelrhodopsin-2 (ChR2) in specific neuronal subpopulations. Members of the population are identified by their response to a brief flash of blue light. This technique &#8211; termed &#8220;PINP&#8221;, or Photostimulation-assisted Identification of Neuronal Populations &#8211; can be implemented with standard extracellular recording equipment. It can serve as an inexpensive and accessible alternative to calcium imaging or visually-guided patching, for the purpose of targeting extracellular recordings to genetically-identified cells. Here we provide a set of guidelines for optimizing the method in everyday practice. We refined our strategy specifically for targeting parvalbumin-positive (PV+) cells, but have found that it works for other interneuron types as well, such as somatostatin-expressing (SOM+) and calretinin-expressing (CR+) interneurons.

A Guide to In vivo Single-unit Recording from Optogenetically Identified Cortical Inhibitory Interneurons

Here we describe our strategy for obtaining stable, well-isolated single-unit recordings from identified inhibitory interneurons in the anesthetized mouse cortex. Neurons expressing ChR2 are identified by their response to blue light. The method uses standard extracellular recording equipment, and serves as an inexpensive alternative to calcium imaging or visually-guided patching.

A major challenge in neurophysiology has been to characterize the response properties and function of the numerous inhibitory cell types in the cerebral ...

Minimally-invasive Technique for Injection into Rat Optic Nerve

The rat optic nerve is a useful model for stem cell regeneration research. Direct injection into the rat optic nerve allows delivery into the central nervous system in a minimally-invasive surgery without bone removal. This technique describes an approach to visualization and direct injection of the optic nerve following minor fascial dissection from the orbital ridge, using a conjunctival traction suture to gently pull the eye down and out. Representative examples of an injected optic nerve show successful injection of dyed beads.

Direct injection into the rat optic nerve is useful for regenerative research. We demonstrate a minimally-invasive technique for direct injection into a rat optic nerve that does not involve opening the skull. Using this method, surgical complications are minimized and recovery is more rapid.

The rat optic nerve is a useful model for stem cell regeneration research. Direct injection into the rat optic nerve allows delivery into the central ...

Visual Evoked Potential Recording in a Rat Model of Experimental Optic Nerve Demyelination

The visual evoked potential (VEP) recording is widely used in clinical practice to assess the severity of optic neuritis in its acute phase, and to monitor the disease course in the follow-up period. Changes in the VEP parameters closely correlate with pathological damage in the optic nerve. This protocol provides a detailed description about the rodent model of optic nerve microinjection, in which a partial demyelination lesion is produced in the optic nerve. VEP recording techniques are also discussed. Using skull implanted electrodes, we are able to acquire reproducible intra-session and between-session VEP traces. VEPs can be recorded on individual animals over a period of time to assess the functional changes in the optic nerve longitudinally. The optic nerve demyelination model, in conjunction with the VEP recording protocol, provides a tool to investigate the disease processes associated with demyelination and remyelination, and can potentially be employed to evaluate the effects of new remyelinating drugs or neuroprotective therapies.

Focal demyelination is induced in the optic nerve using lysolecithin microinjection. Visual evoked potentials are recorded via skull electrodes implanted over the visual cortex to examine the signal conduction along the visual pathway in vivo. This protocol details the surgical procedures underlying electrode implantation and optic nerve microinjection.

The visual evoked potential (VEP) recording is widely used in clinical practice to assess the severity of optic neuritis in its acute phase, and to ...

Determination of Photoreceptor Cell Spectral Sensitivity in an Insect Model from In Vivo Intracellular Recordings

Intracellular recording is a powerful technique used to determine how a single cell may respond to a given stimulus. In vision research, intracellular recording has historically been a common technique used to study sensitivities of individual photoreceptor cells to different light stimuli that is still being used today. However, there remains a dearth of detailed methodology in the literature for researchers wishing to replicate intracellular recording experiments in the eye. Here we present the insect as a model for examining eye physiology more generally. Insect photoreceptor cells are located near the surface of the eye and are therefore easy to reach, and many of the mechanisms involved in vision are conserved across animal phyla. We describe the basic procedure for in vivo intracellular recording of photoreceptor cells in the eye of a butterfly, with the goal of making this technique more accessible to researchers with little prior experience in electrophysiology. We introduce the basic equipment needed, how to prepare a live butterfly for recording, how to insert a glass microelectrode into a single cell, and finally the recording procedure itself. We also explain the basic analysis of raw response data for determining spectral sensitivity of individual cell types. Although our protocol focuses on determining spectral sensitivity, other stimuli (e.g., polarized light) and variations of the method are applicable to this setup.

Determination of Photoreceptor Cell Spectral Sensitivity in an Insect Model from In Vivo Intracellular Recordings

The electrophysiological technique of intracellular recording is demonstrated and used to determine spectral sensitivities of single photoreceptor cells in the compound eye of a butterfly.

Intracellular recording is a powerful technique used to determine how a single cell may respond to a given stimulus. In vision research, intracellular ...

Acute In Vivo Electrophysiological Recordings of Local Field Potentials and Multi-unit Activity from the Hyperdirect Pathway in Anesthetized Rats

Converging evidence shows that many neuropsychiatric diseases should be understood as disorders of large-scale neuronal networks. To better understand the pathophysiological basis of these diseases, it is necessary to precisely characterize in which way the processing of information is disturbed between the different neuronal parts of the circuit. Using extracellular in vivo electrophysiological recordings, it is possible to accurately delineate neuronal activity within a neuronal network. The application of this method has several advantages over alternative techniques, e.g., functional magnetic resonance imaging and calcium imaging, as it allows a unique temporal and spatial resolution and does not rely on genetically engineered organisms. However, the use of extracellular in vivo recordings is limited since it is an invasive technique that cannot be universally applied. In this article, a simple and easy to use method is presented with which it is possible to simultaneously record extracellular potentials such as local field potentials and multiunit activity at multiple sites of a network. It is detailed how a precise targeting of subcortical nuclei can be achieved using a combination of stereotactic surgery and online analysis of multi-unit recordings. Thus, it is demonstrated, how a complete network such as the hyperdirect cortico-basal ganglia loop can be studied in anesthetized animals in vivo.

Acute In Vivo Electrophysiological Recordings of Local Field Potentials and Multi-unit Activity from the Hyperdirect Pathway in Anesthetized Rats

In this study, the methodology is presented on how to perform multi-site in vivo electrophysiological recordings from the hyperdirect pathway under urethane anesthesia.

Converging evidence shows that many neuropsychiatric diseases should be understood as disorders of large-scale neuronal networks. To better understand the ...

Simultaneous Recordings of Cortical Local Field Potentials, Electrocardiogram, Electromyogram, and Breathing Rhythm from a Freely Moving Rat

Monitoring the physiological dynamics of the brain and peripheral tissues is necessary for addressing a number of questions about how the brain controls body functions and internal organ rhythms when animals are exposed to emotional challenges and changes in their living environments. In general experiments, signals from different organs, such as the brain and the heart, are recorded by independent recording systems that require multiple recording devices and different procedures for processing the data files. This study describes a new method that can simultaneously monitor electrical biosignals, including tens of local field potentials in multiple brain regions, electrocardiograms that represent the cardiac rhythm, electromyograms that represent awake/sleep-related muscle contraction, and breathing signals, in a freely moving rat. The recording configuration of this method is based on a conventional micro-drive array for cortical local field potential recordings in which tens of electrodes are accommodated, and the signals obtained from these electrodes are integrated into a single electrical board mounted on the animal's head. Here, this recording system was improved so that signals from the peripheral organs are also transferred to an electrical interface board. In a single surgery, electrodes are first separately implanted into the appropriate body parts and the target brain areas. The open ends of all of these electrodes are then soldered to individual channels of the electrical board above the animal's head so that all of the signals can be integrated into the single electrical board. Connecting this board to a recording device allows for the collection of all of the signals into a single device, which reduces experimental costs and simplifies data processing, because all data can be handled in the same data file. This technique will aid the understanding of the neurophysiological correlates of the associations between central and peripheral organs.

This study introduces a method for the simultaneous recording of local field potentials in the brain, electrocardiograms, electromyograms, and breathing signals of a freely moving rat. This technique, which reduces experimental costs and simplifies data analysis, will contribute to the understanding of the interactions between the brain and peripheral organs.

Monitoring the physiological dynamics of the brain and peripheral tissues is necessary for addressing a number of questions about how the brain controls ...

Investigating Object Representations in the Macaque Dorsal Visual Stream Using Single-unit Recordings

Previous studies have shown that neurons in parieto-frontal areas of the macaque brain can be highly selective for real-world objects, disparity-defined curved surfaces, and images of real-world objects (with and without disparity) in a similar manner as described in the ventral visual stream. In addition, parieto-frontal areas are believed to convert visual object information into appropriate motor outputs, such as the pre-shaping of the hand during grasping. To better characterize object selectivity in the cortical network involved in visuomotor transformations, we provide a battery of tests intended to analyze the visual object selectivity of neurons in parieto-frontal regions.

A detailed protocol to analyze object selectivity of parieto-frontal neurons involved in visuomotor transformations is presented.

Previous studies have shown that neurons in parieto-frontal areas of the macaque brain can be highly selective for real-world objects, disparity-defined ...