Funding was provided by NIH MH-64611 and NARSAD Young Investigator Award. The authors would also like to acknowledge Adam Beagley, Mark Dikopf, and Ben Smith for their technical assistance.

SU-8 mold fabrication
Master preparation
<ol>
<li>The SU-8 master on silicon wafer substrate is prepared using a two-step standard negative resist lithography process.</li>
<li>The alignment marks on the silicon wafer are removed using a razor blade as the height of these structures (located along the outer periphery of the wafer) is more than the actual device structures. </li>
<li>The silicon wafer is then cleaned using isopropyl alcohol and dried in a stream of N2. Support pillars made out of tape with thickness less than the tallest device structure replace the alignment marks on four sides of the wafer. Note: If the support pillars height is more than the tallest device structures, the through holes are not formed in the PDMS mold. </li>
<li>The master silicon wafer is placed on a hot plate at the room temperature.</li>
</ol>
PDMS solution preparation
<ol>
<li>Four grams of polydimethylsiloxane (PDMS) solution is prepared by thoroughly mixing 10 parts of silicone elastomer with 1 part of curing agent. Note: Make sure that the two solutions are mixed uniformly to obtain similar physical properties throughout the PDMS mold. </li>
<li>The bubbles generated in the PDMS solution during the mixing process are removed using a vacuum desiccator.</li>
</ol>
PDMS coating and curing
<ol>
<li>The bubble-free PDMS solution is slowly dispensed onto the SU-8 master making sure that bubbles are not generated during the dispensing process.</li>
<li>One end of a write-on transparency film is then placed on the hot plate and slowly placed on the PDMS solution to evenly spread the PDMS onto the SU-8 master. Any bubbles generated during this process need to be removed using a probe. [Note: Do not lift the transparency to prevent generation of more bubbles.] </li>
<li>A borofloat slab is placed on top of the transparency sheet to apply uniform pressure. Gentle pressure is applied on the top surface of the tallest circular structures (located midway of the channel lengths and centered along the width of the channels) such that there is minimal or no PDMS sandwiched between the transparency and the SU-8 surface of the circular structures.</li>
<li>Three more borofloat slabs are placed on top of the silicon wafer-borofloat slab sandwich to apply constant pressure on the top surface of the circular opening structures before and during the curing process.</li>
<li>The temperature of the hot plate is then increased to 75&deg;C and the PDMS is cured at this temperature for 1 hour. The hot plate is brought to a temperature of 50&deg;C.</li>
<li>The slabs are removed and the transparency is gently removed leaving behind the master and the thin PDMS sheet coated on top of it.</li>
</ol>
Construction of the microfluidic device
Removal of PDMS sheet from master
<ol>
<li>The outer boundary of the perfusion chamber is carved out on the PDMS sheet using a razor blade after aligning the ports on the perfusion chamber with the ports on the SU-8 master.</li>
<li>The PDMS sheet is then gently removed from the master, pulling along the length of the channels to prevent tearing of PDMS. The PDMS sheet is placed on a transparency sheet with the microfluidic network surface facing upwards.</li>
<li>The inlet and outlet ports are then made using a cork borer.</li>
</ol>
Bonding of PDMS sheet to glass coverslip
<ol>
<li>The bonding surface of the PDMS sheet (the surface containing the microfluidic network) and a glass coverslip are then gently cleaned using a 3M scotch tape, placed on a sheet of transparency, and finally placed in the O2 plasma chamber.</li>
<li>The bonding surfaces are treated with 165 Watts plasma for 10 s. The plasma treated surface of the glass coverslip is immediately bonded to the plasma treated surface of the PDMS sheet. Note: Apply gentle pressure on the glass surface to remove any air bubbles trapped between the bonding surfaces. </li>
<li>Allow 5 minutes to obtain good bonding between the PDMS and glass. After 5 minutes gently remove the transparency on which the PDMS sheet was placed for the bonding process.</li>
<li>The microfluidic device is placed in the oxygen plasma system to make the channels hydrophilic. The plasma treatment is done at 165 Watts for 1 minute.</li>
</ol>
Integration of microfluidic device and perfusion chamber
Preparation of the perfusion chamber
<ol>
<li>An off-the-shelf perfusion chamber was ordered, and inlet and outlet ports were drilled so that when the microfluidic device and the chamber are bonded, the ports on the chamber and the device are aligned. The bottom surface of the perfusion chamber is coated with PDMS to obtain a tight seal between the chamber and the microfluidic device.</li>
<li>A write-on transparency sheet is placed on a hot plate at the room temperature.</li>
<li>One gram PDMS solution is prepared in a process similar to that described earlier. The bubble-free PDMS solution is then slowly dispensed onto the transparency sheet avoiding generation of bubbles.</li>
<li>The perfusion chamber is then placed on the PDMS solution.</li>
<li>A borofloat slab is then placed on top of the chamber to apply uniform pressure and to obtain a thin coating of PDMS on the bottom surface of the chamber.</li>
<li>The temperature of the hot plate is then increased to 75&deg;C and the PDMS is cured at this temperature for 1 hour.</li>
</ol>
Bonding of microfluidic device and perfusion chamber
<ol>
<li>The slab is removed and the transparency is gently removed leaving behind the perfusion chamber and the thin PDMS sheet coated on its bottom surface. Unwanted PDMS is removed using a razor blade and a sharp tip probe for PDMS removal from access ports.</li>
<li>The PDMS surface of the microfluidic device and the PDMS bottom surface of the chamber are then gently cleaned using a 3M tape, placed on a sheet of transparency, and finally placed in the oxygen plasma chamber.</li>
<li>The surfaces are treated with 165 Watts plasma for 10 s. The PDMS coated surface of the chamber is immediately bonded to the PDMS surface of the microfluidic device. Note: Apply gentle pressure on the glass surface to remove any air bubbles trapped between the bonding surfaces. </li>
<li>Immediately before the use, the device is placed in the oxygen plasma system to make the channels hydrophilic. The plasma treatment is done at 165 Watts for 1 minute.</li>
</ol>
Exposing brain slices to neurochemical microenvironment using the microfluidic device
<ol>
<li>The hydrophilic microchannels of the (microfluidic device)-(perfusion chamber) combination are filled with standard ACSF (Artificial Cerebral Spinal Fluid) solution.</li>
<li>Dispense small drops of ACSF solution at the inlet ports and allow the solution to be wicked up into the channels. Remove any bubbles left using a syringe from the outlet port. Dispense a large drop of ACSF solution at the outlet port to allow passive pumping of fluids from inlet to outlet ports of the microfluidic device. Note: Care should be taken to remove all bubbles from the channels to allow flow of fluids using passive pumping method. </li>
<li>Fix the (microfluidic device)-(perfusion chamber) combo in the plain platform and fix the plain platform into the microscope adapter.</li>
<li>Connect the standard inlet and outlet (suction) tubing to the perfusion chamber for continuous perfusion of the brain slice with standard ACSF solution. The ACSF solution is continuously aspirated with 95% O2-5% CO2. Note: Adjust the position of the suction tubing to maintain constant level of ACSF in the bath of the perfusion chamber. </li>
<li>Once the perfusion chamber is filled with ACSF solution, place a brain slice in the perfusion chamber using a dropper. Using a probe, position the brain slice above the circular openings in the microfluidic device. Once the brain slice is at the desired position over the circular openings, use a slice anchor to immobilize the brain slice.</li>
<li>The microfluidic device can now be used to expose the brain slices (placed in the perfusion chamber and on top of the microfluidic network) to various neurotransmitters using passive pumping of fluids.</li>
</ol>

<ol>
	<li>Blake, A. J., Pearce, T. M., Rao, N. S., Johnson, S. M., Williams, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multilayer+PDMS+microfluidic+chamber+for+controlling+brain+slice+microenvironment.">Multilayer PDMS microfluidic chamber for controlling brain slice microenvironment.</a> Lab on a Chip. 7, 842-849 (2007).</li><li>Walker, G. M., Beebe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+passive+pumping+method+for+microfluidic+devices.">A passive pumping method for microfluidic devices.</a> Lab on a Chip. 2, 131-134 (2002).</li></ol>

The authors are open to collaborations involving the demonstrated microfluidic technology to different fields of biology.

Existing macroscale or microscale brain slice perfusion chambers are limited in terms of the spatial resolution they provide to expose brain slices with neurotransmitters. The microfluidic device technology demonstrated here overcomes this limitation using simple bioMEMS techniques. It is anticipated that the simplicity in the fabrication of the microfluidic device and the ease in integrating it with existing electrophysiology setups will allow widespread application of the demonstrated device technology. Interesting exp...

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		<div>
		<table border="1">
		<thead>
		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
		</thead>
		<tbody>
		
<tr>
<td>RC-26GPL</td>
<td>Tool</td>
<td>Warner Instruments</td>
<td>W2-64-0236</td>
<td>Low Profile Large Bath RC-26GLP Recording Chamber</td>
</tr>
<tr>
<td>SHD-26GH/10</td>
<td>Tool</td>
<td>Warner Instruments</td>
<td>W2-64-0253</td>
<td>Stainless steel slice hold-down for RC-26G, 1.0 mm thread spacing </td>
</tr>
<tr>
<td>PDMS (polydimethylsiloxane)</td>
<td>Reagent</td>
<td>Dow Corning</td>
<td>Sylgard 184</td>
<td>Silicone Elastomer Kit</td>
</tr>
<tr>
<td>Plasma Preen-II 862</td>
<td>Tool</td>
<td>Plasmatic Systems, Inc.</td>
<td>&nbsp;</td>
<td>Microwave plasma system</td>
</tr>
<tr>
<td>Model P-1</td>
<td>Tool</td>
<td>Warner Instruments</td>
<td>W2-64-0277</td>
<td>Series 20 Plain Platform, Model P-1</td>
</tr>
<tr>
<td>SA-NIK</td>
<td>Tool</td>
<td>Warner Instruments</td>
<td>W2-64-0291</td>
<td>Adapter for Nikon Diaphot/TE200/TE2000, SA-NIK</td>
</tr>
<tr>
<td>Oxygenated, heated ACSF (Artificial cerebro-spinal fluid)</td>
<td>Reagent</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>Exact composition will vary with application</td>
</tr>		</tbody>
		</table>
		</div>

brain slice stimulation using a microfluidic network and standard perfusion chamber

We have demonstrated the fabrication of a two-level microfluidic device that can be easily integrated with existing electrophysiology setups. The two-level microfluidic device is fabricated using a two-step standard negative resist lithography process 1. The first level contains microchannels with inlet and outlet ports at each end. The second level contains microscale circular holes located midway of the channel length and centered along with channel width. Passive pumping method is used to pump fluids from the inlet port to the outlet port 2. The microfluidic device is integrated with off-the-shelf perfusion chambers and allows seamless integration with the electrophysiology setup. The fluids introduced at the inlet ports flow through the microchannels towards the outlet ports and also escape through the circular openings located on top of the microchannels into the bath of the perfusion. Thus the bottom surface of the brain slice placed in the perfusion chamber bath and above the microfluidic device can be exposed with different neurotransmitters. The microscale thickness of the microfluidic device and the transparent nature of the materials [glass coverslip and PDMS (polydimethylsiloxane)] used to make the microfluidic device allow microscopy of the brain slice. The microfluidic device allows modulation (both spatial and temporal) of the chemical stimuli introduced to the brain slice microenvironments.

Watch this Scientific Journal Video about Brain Slice Stimulation Using a Microfluidic Network and Standard Perfusion Chamber at JoVE.com

Brain Slice Stimulation Using a Microfluidic Network and Standard Perfusion Chamber

We demonstrate fabrication of a simple microfluidic device that can be integrated with standard electrophysiology setups to expose microscale surfaces of a brain slice in a well controlled manner to different neurotransmitters.

We have demonstrated the fabrication of a two-level microfluidic device that can be easily integrated with existing electrophysiology setups. The ...

brain-slice-stimulation-using-microfluidic-network-standard-perfusion

Research

JoVE Journal

Biology

10.8K vistas.  University of Illinois, Chicago. Se demuestra la fabricación de un dispositivo de microfluidos sencillos que pueden ser integrados con el estándar de configuraciones de electrofisiología para exponer las superficies a microescala de un trozo del cerebro de una manera bien controlada para los diferentes neurotransmisores.

Video: Brain Slice Stimulation Using a Microfluidic Network and Standard Perfusion Chamber

Fabrication of a Microfluidic Device for the Compartmentalization of Neuron Soma and Axons

In this video, we demonstrate the technique of soft lithography with polydimethyl siloxane (PDMS) which we use to fabricate a microfluidic device for culturing neurons. Previously, a silicon wafer was patterned with the design for the neuron microfluidic device using SU-8 and photolithography to create a master mold, or what we simply refer to as a "master". Next, we pour the silicon polymer PDMS on top of the master which is then cured by heating the PDMS to 80&deg;C for 1 hour. The PDMS forms a negative mold of the device. The PDMS is then carefully cut and lifted away from the master. Holes are punched where the reservoirs will be and the excess PDMS trimmed away from the device. Nitrogen is used to blow away any excess debris from the device. At this point the devices are now ready for use and can either bonded to corning No. 1 cover glass with a plasma sterilizer/cleaner or can be reversibly bound to the cover glass by simply placing the device on top of the cover glass. The reversible bonding of the device to glass is covered in a separate video and requires first that the device be sterilized either with 70% ethanol or by autoclaving. Plasma treating sterilizes the devices so no further treatment is necessary. It is, however, important, when plasma-treating the devices, to add liquid to the devices within 10 minutes of the plasma treatment while the surfaces are still hydrophilic. Waiting longer than 10 minutes to add liquid to the device makes it difficult for the liquid to enter the device. The neuron devices are typically plasma-bound to cover glass and 0.5 mg/ml poly-L-lysine (PLL) in pH 8.5 borate buffer is immediately added to the device. After a minimum of 3 hours incubating with PLL, the devices are washed with dH2O water a minimum of 3 times with at least 15 minutes between each wash. Next, the water is removed and fresh media is added to the device. At this point the device is ready for use. It is important to remember at this point to never remove all the media from the device. Always leave media in the main channel.

In this video we demonstrate the technique of soft lithography with polydimethyl siloxane (PDMS) which we use to farbricate a microfluidic device for culturing neurons.

In this video, we demonstrate the technique of soft lithography with polydimethyl siloxane (PDMS) which we use to fabricate a microfluidic device for ...

Preparing E18 Cortical Rat Neurons for Compartmentalization in a Microfluidic Device

In this video, we demonstrate the preparation of E18 cortical rat neurons. E18 cortical rat neurons are obtained from E18 fetal rat cortex previously dissected and prepared. The E18 cortex is, upon dissection, immediately dissociated into individual neurons. It is possible to store E18 cortex in Hibernate E buffer containing B27 at 4&deg;C for up to a week before the dissociation is performed. However, there will be a drop in cell viability. Typically we obtain our E18 Cortex fresh. It is transported to the lab in ice cold Calcium free Magnesium free dissection buffer (CMFM). Upon arrival, trypsin is added to the cortex to a final concentration of 0.125%. The cortex is then incubated at 37&deg;C for 8 minutes. DMEM containing 10% FBS is added to the cortex to stop the reaction. The cortex is then centrifuged at 2500 rpm for 2 minutes. The supernatant is removed and 2 ml of Neural Basal Media (NBM) containing 2% B27 (vol/vol) and 0.25% Glutamax (vol/vol) is added to the cortex which is then re-suspended by pipetting up and down. Next, the cortex is triturated with previously fire polished glass pipettes, each with a successive smaller opening. After triturating, the cortex is once again centrifuged at 2500 rpm for 2 minutes. The supernatant is then removed and the cortex pellet re-suspended with 2 ml of NBM containing B27 and Glutamax. The cell suspension is then passed through a 40 um nylon cell strainer. Next the cells are counted. The neurons are now ready for loading into the neuron microfluidic device.

In this video we demonstrate the preparation of E18 Cortical Rat Neurons.

In this video, we demonstrate the preparation of E18 cortical rat neurons. E18 cortical rat neurons are obtained from E18 fetal rat cortex previously ...

CD4+ T-Lymphocyte Capture Using a Disposable Microfluidic Chip for HIV

Cell Capture Using a Microfluidic Device

Assessing Neural Stem Cell Motility Using an Agarose Gel-based Microfluidic Device

While microfluidic technology is reaching a new level of maturity for macromolecular assays, cell-based assays are still at an infant stage1. This is largely due to the difficulty with which one can create a cell-compatible and steady microenvironment using conventional microfabrication techniques and materials. We address this problem via the introduction of a novel microfabrication material, agarose gel, as the base material for the microfluidic device. Agarose gel is highly malleable, and permeable to gas and nutrients necessary for cell survival, and thus an ideal material for cell-based assays. We have shown previously that agarose gel based devices have been successful in studying bacterial and neutrophil cell migration2. In this report, three parallel microfluidic channels are patterned in an agarose gel membrane of about 1mm thickness. Constant flows with media/buffer are maintained in the two side channels using a peristaltic pump. Cells are maintained in the center channel for observation. Since the nutrients and chemicals in the side channels are constantly diffusing from the side to center channel, the chemical environment of the center channel is easily controlled via the flow along the side channels. Using this device, we demonstrate that the movement of neural stem cells can be monitored optically with ease under various chemical conditions, and the experimental results show that the over expression of epidermal growth factor receptors (EGFR) enhances the motility of neural stem cells. Motility of neural stem cells is an important biomarker for assessing cells aggressiveness, thus tumorigenic factor3. Deciphering the mechanism underlying NSC motility will yield insight into both disorders of neural development and into brain cancer stem cell invasion.

We demonstrate that the over expression of epidermal growth factor receptors (EGFR) enhances the motility of neural stem cells(NSCs) using a novel agarose gel based microfluidic device. This technology can be readily adaptable to other mammalian cell systems where cell sources are scarce, such as human neural stem cells, and the turn around time is critical.

While microfluidic technology is reaching a new level of maturity for macromolecular assays, cell-based assays are still at an infant stage1. This is ...

Trypsinizing and Subculturing Mammalian Cells

As cells reach confluency, they must be subcultured or passaged. Failure to subculture confluent cells results in reduced mitotic index and eventually in cell death. The first step in subculturing is to detach cells from the surface of the primary culture vessel by trypsinization or mechanical means. The resultant cell suspension is then subdivided, or reseeded, into fresh cultures. Secondary cultures are checked for growth and fed periodically, and may be subsequently subcultured to produce tertiary cultures. The time between passaging of cells varies with the cell line and depends on the growth rate.

As cells reach confluency, they must be subcultured or passaged. This video will demonstrate a procedure for subculturing both adherent and suspension cells.

As cells reach confluency, they must be subcultured or passaged. Failure to subculture confluent cells results in reduced mitotic index and eventually in ...

Freezing, Thawing, and Packaging Cells for Transport

Cultured mammalian cells are used extensively in cell biology studies. It requires a number of special skills in order to be able to preserve the structure, function, behavior, and biology of the cells in culture. This video describes the basic skills required to freeze and store cells and how to recover frozen stocks. 

Cultured mammalian cells are used extensively in cell biology studies. This video describes the basic skills required to freeze and store cells and how to recover frozen stocks.

Cultured mammalian cells are used extensively in cell biology studies. It requires a number of special skills in order to be able to preserve the ...

The Microfluidic Probe: Operation and Use for Localized Surface Processing

Microfluidic devices allow assays to be performed using minute amounts of sample and have recently been used to control the microenvironment of cells. Microfluidics is commonly associated with closed microchannels which limit their use to samples that can be introduced, and cultured in the case of cells, within a confined volume. On the other hand, micropipetting system have been used to locally perfuse cells and surfaces, notably using push-pull setups where one pipette acts as source and the other one as sink, but the confinement of the flow is difficult in three dimensions. Furthermore, pipettes are fragile and difficult to position and hence are used in static configuration only. 
The microfluidic probe (MFP) circumvents the constraints imposed by the construction of closed microfluidic channels and instead of enclosing the sample into the microfluidic system, the microfluidic flow can be directly delivered onto the sample, and scanned across the sample, using the MFP. . The injection and aspiration openings are located within a few tens of micrometers of one another so that a microjet injected into the gap is confined by the hydrodynamic forces of the surrounding liquid and entirely aspirated back into the other opening. The microjet can be flushed across the substrate surface and provides a precise tool for localized deposition/delivery of reagents which can be used over large areas by scanning the probe across the surface. 
In this video we present the microfluidic probe1 (MFP). We explain in detail how to assemble the MFP, mount it atop an inverted microscope, and align it relative to the substrate surface, and finally show how to use it to process a substrate surface immersed in a buffer.

In this video we present the microfluidic probe1 (MFP). We explain in detail how to assemble the MFP, mount it atop an inverted microscope, and align it relative to the substrate surface, and finally show how to use it to process a substrate surface immersed in a buffer solution.

Microfluidic devices allow assays to be performed using minute amounts of sample and have recently been used to control the microenvironment of cells. ...

Platelet Adhesion and Aggregation Under Flow using Microfluidic Flow Cells

Platelet aggregation occurs in response to vascular injury where the extracellular matrix below the endothelium has been exposed. The platelet adhesion cascade takes place in the presence of shear flow, a factor not accounted for in conventional (static) well-plate assays. This article reports on a platelet-aggregation assay utilizing a microfluidic well-plate format to emulate physiological shear flow conditions. Extracellular proteins, collagen I or von Willebrand factor are deposited within the microfluidic channel using active perfusion with a pneumatic pump. The matrix proteins are then washed with buffer and blocked to prepare the microfluidic channel for platelet interactions. Whole blood labeled with fluorescent dye is perfused through the channel at various flow rates in order to achieve platelet activation and aggregation. Inhibitors of platelet aggregation can be added prior to the flow cell experiment to generate IC50 dose response data.

The platelet adhesion cascade takes place in the presence of shear flow, a factor not accounted for in conventional (static) well-plate assays. This article reports on a platelet-aggregation assay utilizing a microfluidic well-plate format to emulate physiological shear flow conditions.

Platelet aggregation occurs in response to vascular injury where the extracellular matrix below the endothelium has been exposed. The platelet adhesion ...

Mapping the After-effects of Theta Burst Stimulation on the Human Auditory Cortex with Functional Imaging

Auditory cortex pertains to the processing of sound, which is at the basis of speech or music-related processing1. However, despite considerable recent progress, the functional properties and lateralization of the human auditory cortex are far from being fully understood. Transcranial Magnetic Stimulation (TMS) is a non-invasive technique that can transiently or lastingly modulate cortical excitability via the application of localized magnetic field pulses, and represents a unique method of exploring plasticity and connectivity. It has only recently begun to be applied to understand auditory cortical function 2. 
An important issue in using TMS is that the physiological consequences of the stimulation are difficult to establish. Although many TMS studies make the implicit assumption that the area targeted by the coil is the area affected, this need not be the case, particularly for complex cognitive functions which depend on interactions across many brain regions 3. One solution to this problem is to combine TMS with functional Magnetic resonance imaging (fMRI). The idea here is that fMRI will provide an index of changes in brain activity associated with TMS. Thus, fMRI would give an independent means of assessing which areas are affected by TMS and how they are modulated 4. In addition, fMRI allows the assessment of functional connectivity, which represents a measure of the temporal coupling between distant regions. It can thus be useful not only to measure the net activity modulation induced by TMS in given locations, but also the degree to which the network properties are affected by TMS, via any observed changes in functional connectivity.
Different approaches exist to combine TMS and functional imaging according to the temporal order of the methods. Functional MRI can be applied before, during, after, or both before and after TMS. Recently, some studies interleaved TMS and fMRI in order to provide online mapping of the functional changes induced by TMS 5-7. However, this online combination has many technical problems, including the static artifacts resulting from the presence of the TMS coil in the scanner room, or the effects of TMS pulses on the process of MR image formation. But more importantly, the loud acoustic noise induced by TMS (increased compared with standard use because of the resonance of the scanner bore) and the increased TMS coil vibrations (caused by the strong mechanical forces due to the static magnetic field of the MR scanner) constitute a crucial problem when studying auditory processing. 
This is one reason why fMRI was carried out before and after TMS in the present study. Similar approaches have been used to target the motor cortex 8,9, premotor cortex 10, primary somatosensory cortex 11,12 and language-related areas 13, but so far no combined TMS-fMRI study has investigated the auditory cortex. The purpose of this article is to provide details concerning the protocol and considerations necessary to successfully combine these two neuroscientific tools to investigate auditory processing. 
Previously we showed that repetitive TMS (rTMS) at high and low frequencies (resp. 10 Hz and 1 Hz) applied over the auditory cortex modulated response time (RT) in a melody discrimination task 2. We also showed that RT modulation was correlated with functional connectivity in the auditory network assessed using fMRI: the higher the functional connectivity between left and right auditory cortices during task performance, the higher the facilitatory effect (i.e. decreased RT) observed with rTMS. However those findings were mainly correlational, as fMRI was performed before rTMS. Here, fMRI was carried out before and immediately after TMS to provide direct measures of the functional organization of the auditory cortex, and more specifically of the plastic reorganization of the auditory neural network occurring after the neural intervention provided by TMS. 
Combined fMRI and TMS applied over the auditory cortex should enable a better understanding of brain mechanisms of auditory processing, providing physiological information about functional effects of TMS. This knowledge could be useful for many cognitive neuroscience applications, as well as for optimizing therapeutic applications of TMS, particularly in auditory-related disorders.

Auditory processing is the basis of speech and music-related processing. Transcranial Magnetic Stimulation (TMS) has been used successfully to study cognitive, sensory and motor systems but has rarely been applied to audition. Here we investigated TMS combined with functional Magnetic Resonance Imaging to understand the functional organization of auditory cortex.

Auditory cortex pertains to the processing of sound, which is at the basis of speech or music-related processing1. However, despite considerable recent ...