This article provides an overview of a multi-modal brain mapping program designed to identify regions of the brain that support critical cognitive functions in individual neurosurgery patients.
The Translational Brain Mapping Program at the University of Rochester is an interdisciplinary effort that integrates cognitive science, neurophysiology, neuroanesthesia, and neurosurgery. Patients who have tumors or epileptogenic tissue in eloquent brain areas are studied preoperatively with functional and structural MRI, and intraoperatively with direct electrical stimulation mapping. Post-operative neural and cognitive outcome measures fuel basic science studies about the factors that mediate good versus poor outcome after surgery, and how brain mapping can be further optimized to ensure the best outcome for future patients. In this article, we describe the interdisciplinary workflow that allows our team to meet the synergistic goals of optimizing patient outcome and advancing scientific understanding of the human brain.
Neurosurgical interventions to remove brain tumors or epileptogenic tissue adjacent to brain areas that support critical cognitive functions must balance the clinical objective of the surgery (remove as much tumor, or epileptogenic tissue as possible) against damage to healthy tissue that could cause neurologic deficits. In the context of brain tumor surgery, this balance is referred to as the onco-functional balance. On the 'onco' side of the balance, surgeons want to remove as much of the tumor as possible, as rates of 'gross total tumor resection' are linked to longer survival1,2. On the 'functional' side, removal of tumors can damage cortical and subcortical substrates of cognition; post-operative difficulties can involve language, action, vision, hearing, touch or movement, depending on the neural system(s) affected. The onco-functional balance is critically important because increased morbidity is associated with i) lower quality of life, ii) increased post-operative complications that can increase mortality (e.g., patients who can no longer move are at a higher risk of blood clots3,4). The tension inherent in the 'onco-functional' balance in the setting of brain tumor surgery translates as well to epilepsy surgery — there the balance is between the clinical objective of removing all tissue that is generating seizures, while not removing tissue that supports critical functions.
At a broad level, functional neuroanatomy is highly stereotyped from individual to individual. However, there can be a high degree of individual variability in the precise (i.e., mm to mm) location of higher cortical functions. In addition, it is generally recognized that the presence of cortical or subcortical pathology can spur cortical reorganization, although the principles that drive such reorganization are poorly understood5. Neurosurgical interventions proceed millimeter by millimeter. It is thus critical to map each patient's brain, in detail and with sensitivity and precision, in order to understand which regions in that specific patient support which sensory, cognitive and motor functions6.
The Program for Translational Brain Mapping at the University of Rochester has been engineered to meet the needs of personalized brain mapping in the setting of a high through-put practice spanning multiple academic surgeons. The synergistic goals of the Brain Mapping Program are to i) use the tools of cognitive neuroscience to advance personalized neuromedicine, in the form of patient-specific functional brain maps, and ii) use the clinical preparation of neurosurgical interventions to test mechanistic hypotheses about how the human brain functions.
The activities shown in the video and described herein fall within a greater-than-minimal-risk IRB at the University of Rochester Medical Center.
1. Recruitment
2. Pre-Operative MRI mapping
3. Neuropsychological testing
4. Neuroanesthesia and ergonomics of intraoperative language mapping
5. Procedures for acquiring research-grade data during intraoperative direct electrical stimulation mapping
Figure 2, Figure 3, and Figure 4 present representative results of pre-operative functional and structural mapping for three patients with tumors that were adjacent to eloquent regions of the brain. The findings shown in Figure 2, Figure 3, and Figure 4 are intended to be illustrative (rather than an exhaustive summary) of the types of maps that are generated for each patient. Details on the cases presented in Figure 2, Figure 3, and Figure 4 can be found in: Figure 2 (Chernoff, Teghipco, Garcea, Sims, Belkhir, Paul, Tivarus, Smith, Hintz, Pilcher, Mahon, in press51), Figure 3 (Chernoff, Sims, Smith, Pilcher and Mahon, 201952), and Figure 4 (Garcea et al., 201716). An important consequence of consecutive recruitment of glioma patients into a uniform protocol is that it makes possible group-level analyses that evaluate the effect of brain tumors on network function and organization. As an example of this type of analyses, Figure 5 presents results from a recent study 14 that found that tumors in left parietal cortex modulated neural responses to 'tools' (small manipulable objects) in the temporal lobe, an instance of a more general phenomenon referred to as dynamic diaschesis53.
Figure 1. Overview of Equipment used for extra-operative and intra-operative cognitive testing. (A) Example setup for high through-put cognitive neuropsychological testing as implemented by the Program for Translational Brain Mapping in the Department of Neurosurgery at the University of Rochester Medical Center. Key elements for ensuring that all recruited patients are able to complete all planned tests include: i) a place for patients to sit and complete testing that is fully adjustable to each patient's size, including a chair specifically designed to reduce fatigue, and ii) locating cognitive/behavioral testing physically adjacent to the MRI. These elements allow patients to visit the facility and complete their functional and structural MRI within the same session as core behavioral data are measured. Participants complete more trials with better performance if they are comfortable, especially for older participant populations with other comorbidities that can make sitting for prolonged periods uncomfortable. (B) Equipment used during intraoperative mapping. The image at the left shows a patient before being draped (right is after draping). Before draping, the cognitive science team sets up their equipment, including audio and video recorders of the patient, a monitor positioned in front of the patient's line of sight, and a second monitor positioned so that the person working with the patient can easily see the stimulus at which the patient is currently looking (see 'Procedure' for details). (C) Bipolar Stimulator with registration star attached to record locations of intra-operative stimulation in preoperative MRI DICOM space. Usually at the point in the surgery at which the dura has been retracted and the patient is being awoken from general anesthesia, there are a few minutes in which to register the bipolar stimulator to the field. This must be done by a team member who is scrubbed in to the case (i.e., either attending or resident surgeon or a scrub tech/nurse). It is accomplished by attaching a small registration star to the bipolar stimulator and following the instructions in the cranial navigation system to register a new instrument on the field. Please click here to view a larger version of this figure.
Figure 2. Pre-operative functional MRI and Diffusion Tensor Imaging (DTI) in patient AH with a left inferior parietal glioma that infiltrated the arcuate fasciculus. (A) Pre-operative T1 MRI and 3D reconstruction of the left arcuate fasciculus and glioma. The arcuate fasciculus is shown in orange at a 5% threshold with the tumor reconstructed in blue. (B) Pre-Operative functional MRI. The patient completed several sessions of functional MRI that were each designed to map a function that was anticipated to be adjacent to the area of surgical intervention. All maps are thresholded at FDR q < .05 or better. In blue are voxels that exhibit differential neural responses when naming tools compared to animals; in line with prior studies from our lab using the same stimuli, a robust network is identified involving premotor, parietal, and lateral and ventral temporal areas7,8,9,10,14,15,17,18,19,20,21,22,28. The patient was also asked to carry out a numerosity task in which he had to judge which of two clouds of dots had more dots; the two clouds of dots could either have a similar number of dots (hard comparison, ratio = 0.8) or very different numbers of dots (easy comparison, ratio = 0.25). In green are voxels that exhibit differential neural responses when carrying out the task over hard ratio stimuli (ratio = .8) compared to easy stimuli (ratio = .25 54,55). The patient was also asked to move his hands and feet (either flex/extension or rotate25). In red are voxels that exhibited differential neural responses to movements of the right hand compared to movements of the right foot. Finally, the patient was asked to generate as many items as he could think of in 30 seconds from various categories (e.g., 'things you do in the kitchen', 'animals', words that start with 'F', etc.). In purple are voxels that exhibited differential neural activity for overt word production compared to fixation/rest. Please click here to view a larger version of this figure.
Figure 3. Pre-Operative white matter tractography of the Frontal Aslant Tract and adjacent u-shaped fibers. Prior experience in the Program for Translational Brain Mapping (Chernoff et al., 201756) with brain mapping in patients with gliomas adjacent to the frontal aslant tract demonstrated that (even partial) transection of this pathway can be associated with dysfluencies in spontaneous speech, while repetition of spoken language can remain intact. That prior experience was used to inform pre-operative mapping of the frontal aslant tract in patient AI11. (A) Coronal slices showing the frontal aslant tract (blue-light blue) and u-shaped fibers (red-yellow). The frontal aslant tract passes just anterior and medial to the glioma. (B) 3D Rendering of frontal aslant tract (blue) and tumor (red) from multiple perspectives. The pre-operative anatomical studies (Panels A and B) indicated that at the end of the tumor resection, it would be possible to define the anterior margin of tumor using direct electrical stimulation mapping. We thus designed a new language task based on our prior experience, specifically to test whether stimulation of the frontal aslant tract disrupted sentence production at the boundaries of grammatical phrases. (C) Direct electrical stimulation of the frontal aslant tract disrupts sentence production differentially at the boundaries of grammatical phrases. The screenshot (Panel C, left) from the video shows the patient, the stimulus with which he was presented, the surgeon's hand holding the bipolar stimulator in contact with the frontal aslant tract at the anterior margin of the tumor, and the location in coronal and sagittal slices of the current stimulation location (red dot) in relation to the frontal aslant tract (blue). The patient's task was to describe the spatial relation of the target shape in relation to the location of a reference shape (for the trial shown, the correct response would be: "The red square is below the red diamond'). We found that stimulation of the frontal aslant tract disrupted sentence production, and differentially so at the start of new grammatical phrases (Panel C, graph at right; for video of the intraoperative mapping procedure in this patient, see www.openbrainproject.org). This observation motivates a novel hypothesis about the role of the frontal aslant tract in sentence production: the Syntagmatic Constraints on Positional Elements (SCOPE) hypothesis11. Please click here to view a larger version of this figure.
Figure 4. Pre-Operative functional and structural MRI and intraoperative direct electrical stimulation mapping in a professional musician with a glioma in the right posterior temporal lobe. (A) Pre-operative fMRI mapping of high-level visual processing, language production, and tool knowledge. The tumor, shaded yellow, was in the right temporal lobe, visible through the right superior temporal sulcus (sulci slightly expanded to facilitate visualization). Because the tumor was located close to motion processing areas in lateral temporal cortex, we localized MT/V5 by comparing neural activity when the patient attended to arrays of moving dots to neural activity elicited by stationary dots; voxels exhibiting differential neural responses for motion compared to static dots are plotted on the purple-white color scale (we are grateful to Duje Tadin for assistance with developing this functional localizer). As for all other cases studied in the Program for Translational Brain Mapping (e.g., Figure 2, Figure 3), voxels exhibiting differential neural responses for naming common pictures are compared to a baseline of viewing phase-scrambled versions of the same images; this is plotted on the green-white color scale. That contrast identified bilateral lateral occipital complex, bilateral middle/superior temporal gyrus, and motor cortex (associated with speech motor activity). Also as in Figure 2, voxels exhibiting differential neural responses when naming 'tools' were found in the left inferior parietal lobule, bilateral superior parietal/dorsal occipital cortex, and the left posterior middle/inferior temporal gyrus (blue-white color scale). Finally, and again as in Figure 2, the patient was asked to complete a verbal fluency word production task. Voxels associated with word generation compared to a resting baseline are plotted on the red-white color scale and were found in the left inferior frontal gyrus (Broca's area), superior temporal/inferior parietal cortex, and the speech motor system. (B) The patient completed multiple functional MRI experiments pre-operatively specifically to map music processing. In one experiment, modeled after prior work from Greg Hickok's lab57, the patient heard short piano melodies and had to hum the melody back, or heard short sentences and had to repeat the sentences back. Plotted on the brain on the red-purple color scale are voxels that exhibited differential neural activity for music than for language. Four Eastman School of Music Graduate students completed the same fMRI experiment; the border of the region identified for the same functional contrast in the matched healthy controls is plotted in green outline. In addition, 10 other neurosurgery patients completed the same experiment, also in the preoperative phase of their treatment. While the proximate goal in those 10 patients was to identify language-responsive areas (thorugh the contrast of language > music), the contrast of music>language identifies a very similar region of the right superior temporal gyrus (borders of the functional region from the 10 control neurosurgery patients are drawn in light blue). (C) Pre-operative probabilistic tractography over DTI data showing the right acoustic radiations and arcuate fasciculus in relation to patient AE's tumor (5% threshold, overlaid on native T2-weighted image). (D) During his surgery, patient AE performed the same task as during fMRI in which he had to listen to short piano melodies and hum them back, or a short sentence and repeat it back. It was found that direct electrical stimulation to the right posterior superior temporal gyrus disrupted performance in the repetition task when performed over melodies (for some trials), but did not affect performance (on any trials) for the same repetition task performed over sentences (see www.openbrainproject.org for videos of intraoperative music mapping). Please click here to view a larger version of this figure.
Figure 5. Demonstration of domain-specific diaschesis: Analysis of the relation of lesion location and stimulus-elicited neural activity across a group of glioma patients studied pre-operatively in the Program for Translational Brain. An important consequence of administering a common set of functional MRI and behavioral studies to all patients who go through the Program for Translational Brain Mapping at the University of Rochester Medical Center is the opportunity to carry out group-level analyses on larger sets of consecutively studied patients. As an example, Figure 5 shows the results of a test of the basic science hypothesis that neural responses to 'tools' in the temporal lobe are modulated online by inputs from parietal cortex. If that hypothesis is correct, then lesions (tumors) in parietal cortex should alter neural responses in the temporal lobe to 'tools', and variance across patients in neural activity to 'tools' in the temporal lobe should be correlated with the presence of lesions (tumors) in parietal cortex. (A) Lesions to parietal cortex are predicted at the group level (logistic regression) from variance across patients in neural responses in the medial fusiform gyrus on the ventral surface of the temporal lobe. (B) Neural responses to tools in the medial fusiform gyrus are predicted at the group level (logistic regression) from variance in whether lesion/tumor involves the anterior Intraparietal Sulcus (aIPS). The findings summarized in panels A and B represent an instance of dynamic diaschesis53, in this case 'domain-specific' dynamic diaschesis, because the relation of lesion location to neural activity is modulated by the type of stimulus being processed (i.e., the relation is present for tools, and not for places, face or animals)-for full details see Garcea and colleagues14. Please click here to view a larger version of this figure.
The knowledge gained from the experience of establishing the Program for Translational Brain Mapping at the University of Rochester can be distilled down into two core elements. First, structured channels of communication were established among cognitive scientists, neuro-oncologists, neuropsychologists, epileptologists, neurophysiologists, neuro-anesthesiologists, neurosurgeons and their respective supporting technicians and administrative support. This allows patients, including urgent high-grade tumor patients, to be referred for pre-operative evaluation with sufficient time to turn analyses around to surgeons prior to the procedure. The second component critical to the success of the Brain Mapping Program has been to fold in training opportunities for undergraduate students, graduate (MS, PhD) students, medical students, as well as neurosurgery, neurology and neuroradiology residents and fellows. The combination of those two elements serve to engage all clinical providers with the scientific objectives of the Brain Mapping Program, and ensures that basic science objectives are intertwined with the clinical goal of optimizing the outcome of every patient.
The authors have nothing to disclose.
This work was supported by NIH Grants R21NS076176, R01NS089069, R01EY028535, and NSF Grant BCS-1349042 to BZM, and by a University of Rochester Center for Visual Science predoctoral training fellowship (NIH training Grant 5T32EY007125-24) to FEG. We are grateful to Keith Parkins for his work on the development of StrongView, which was supported by core grant P30EY00131 to the Center for Visual Science at the University of Rochester Medical School. The Program for Translational Brain Mapping at the University of Rochester was established, in part, with support from Norman and Arlene Leenhouts, and with a grant from the Wilmot Cancer Institute to Drs. Kevin Walter and Bradford Mahon. Information about the Program for Translational Brain Mapping at the University of Rochester Medical Center can be found at: www.tbm.urmc.edu.