The Soundtrack of Surgery

by Tressel Holton

art by Gabriella Mouris

You float through intangibility, untethered from the grip of reality, save for the sensual opening violin of Gustav Holst's “Venus.” Each note seems to dance between your sealed eyelids, electrifying the space between corporeality and nothingness—that is, until the voice of your neurosurgeon shatters the illusion: “How does this feel?” The surgical team is testing the tissue in your auditory cortex, the neural center for hearing, to determine the best technique for treating a small tumor. A vital tool in the operating room, music reinforces awake neurosurgery by charting a course of action that guides the surgeon to success and the patient to safety.

Why would a neurosurgeon, occupied with a complex operation on the brain, take time to play music for their patient? At first, this might seem counterintuitive, but consider a cave diver squeezing through a pitch-black crevice. The cave diver must rely on his sense of touch as well as any cave diving experience if he is to navigate this ordeal. Regardless of his individual skill level, the process of cave diving is a challenge with minimal room for error. If, however, the walls of the cave were suddenly illuminated by bioluminescent algae, the diving process would become significantly easier. In much the same way, music-based patient feedback provides crucial clarity during awake neurosurgery. A simple melody can serve as a guiding light for the surgeon by mapping the patient’s brain, stimulating cognitive activity, or even alleviating patient stress.

Mapping the Mind: Music as a Surgical Tool

Obtaining this clarity involves cognitive mapping, through which the surgeon identifies critical regions of the brain for specific cognitive functions like pitch identification and rhythm tracking [1,2]. Two primary methodologies facilitate this mapping in relation to music: direct electrical stimulation (DES) and functional magnetic resonance imaging (fMRI) [3]. 

DES is an intraoperative technique, meaning that it can be carried out during the actual brain surgery. It requires a neurosurgeon to gently stimulate different areas of the brain with an electrical probe, testing how the patient responds. These probes can inhibit or enhance the firing rate of action potentials, the electrical signals that mediate communication between neurons [4]. Because DES allows for real-time interaction, it pairs seamlessly with intraoperative cognitive tests. A surgeon might, for instance, ask a patient to hum a lullaby, stimulate the auditory cortex with electricity, and then request the lullaby again to observe any changes to brain function [5]. Thanks to local anesthetics, a neurosurgeon can play music and interview their patient while probing areas like the sensorimotor cortex—the strip of brain tissue responsible for processing sensations on our skin—via DES and cognitive testing [6]. These neuropsychological cognitive tests range from linguistic examinations to motor skill checks, providing the surgeon with real-time awareness of the patient’s unique neural structure and designating the “safe areas” for making incisions [7].

fMRI, on the other hand, is largely a preoperative technique. The fMRI technique employs a standard MRI magnet to envelope the brain in a magnetic field that scans for areas of high oxygen concentration, which indicates more blood flow to, and thus more activity in, a particular region of the brain [8]. Its role in surgical planning is particularly evident in complex cases, such as that of a 16-year-old violinist and vocalist in India diagnosed with temporal lobe epilepsy (TLE). TLE seizures can be triggered by any type of intensive sensory overload, especially unexpected auditory stimuli like excessive loudness. This condition threatened both his musical and cognitive abilities, including auditory processing and short-term memory recall—and required an awake craniotomy, a surgical excision of part of the skull.

Prior to operating, the boy’s physician conducted an fMRI while asking him to sing along to classical Indian music played over a speaker. Doing so let the physician determine which regions of the brain were critical for the patient’s musical pursuits via fMRI mapping, guiding the surgeon away from vulnerable areas in the temporal lobe and toward the procedure’s target in an amygdalohippocampectomy [9]. This procedure controls seizures by removing most of the amygdala, the center for emotion regulation, and the hippocampus, which controls memory and motor function. In this case, music functioned as an anatomical GPS, but its surgical applications don’t stop there [10].

Therapeutic Rhythms: The Neuroscience of Relaxing Music

Beyond aiding precision, music also provides an emotionally therapeutic resource for patients grappling with the intensity of surgery. Research from the Erasmus University Medical Center details how patients with awake craniotomies frequently experience high levels of stress during the surgical process [11]. Regional anesthesia inhibits most physical pain, but some patients do exhibit symptoms of distress and psychological pain that are understandable given the turmoil of neurosurgery [12]. It is critical that the surgical team anticipates and responds to patient distress throughout the entire perioperative process—prior to, during, and following the operation. Doing so can minimize both frailty, a medical condition characterized by fatigue and a weakened immune system, and even the risk of postoperative death [13]. To address these struggles, healthcare providers need a reliable and efficient method for measuring postoperative patient wellbeing.

One metric for gauging patient condition is the Karnofsky Performance Status (KPS), which is popular in advanced medical subfields like neurology, oncology, and emergency medicine. The KPS scale predicts a patient’s prognosis, with a 100 indicating peak pain-free performance, a 50 signifying a need for immediate medical attention, and a 0 representing death. The target KPS for recovering craniotomy patients is typically around an 80, a level at which patients can perform daily tasks with little difficulty. Any score lower than 50 represents a significant threat to life or livelihood [14]. Analyzing 859 cases of awake craniotomy over 27 years, a research team at the University of California, San Francisco found 40% of recovery patients to exhibit a KPS of less than 80—not in immediate critical condition, but certainly in a suboptimal state of recovery  [15]. The exact cause of this issue is unknown; speculators attribute it to common surgical errors like wrong procedure errors or postoperative objects being left in the patient’s body [16]. Considering that the craniotomy is a relatively simple procedure in the context of neurosurgery, this low metric is fairly concerning, beckoning researchers to rework the methodologies of awake neurosurgery.

Just as recording artists build tracks from simple melodies and rhythms, neurosurgeons use basic science research—the study of fundamental scientific processes like mitosis or catalysis—to improve postoperative KPS. At its core, neurosurgery is tied to basic neuroscience, which involves innovative developments in our understanding of the brain. Listening to music produces a plethora of dynamic neurological effects, ranging from enhanced levels of neurotransmitters associated with happiness, like serotonin and dopamine, to rhythmic neural entrainment. Entrainment, the alignment of neural patterns with exterior musical rhythms, enhances focus and relaxation by synchronizing interneuronal communication [17]. 

Consider the physics of music: as sound waves strike the tympanic membrane, or eardrum, a series of vibrations pass through your middle and inner ear to a set of microscopic hair cells called stereocilia. These stereocilia convert the incoming vibrational energy into electrical signals, which travel along the auditory nerve. These signals are eventually processed into our perception of music via a section of tissue called the primary auditory cortex (A1), located in the aural supercenter of the temporal lobe [18]. A1 is tonotopically organized, meaning that its various layers simultaneously process increasingly complex features of sound from pitch to rhythm [19]. These processed sensations then travel to the amygdala, the epicenter of emotional function. Aligned with emotional activity in the amygdala, A1 transforms incoming music into a unity of frequencies and rhythms that provide a profound sensory immersion [20]. This is a precise example of entrainment in action that is employed in a type of therapy called a music-based intervention (MBI).

MBI provides surgical patients with a calming musical stimulus to relax the mind, whether in or out of the operating room [21]. Like all forms of art-based medical therapy, MBI is extraordinarily stimulating for higher-level cognitive function and is thus an excellent resource for neurosurgeons seeking to soothe patients’ emotions. Astonishingly, music-based interventions have even been known to reduce or eliminate patient perception of pain in a phenomenon known as analgesia—an interruption in the pathway between a sensory receptor (like skin) and the brain [22]. In a study performed by Queen’s University, non-musician participants were repeatedly presented with thermal pulses of varying intensities and asked to rate their pain. These heat pulses were administered through the thenar eminence, the sensitive neural center adjacent to the thumb on the surface of the palm, meaning that a warmer pulse should induce a greater pain response. The participants were permitted to listen to a curated playlist of their favorite tunes (self-selected music is more likely to stimulate the reward & pleasure centers of the brain) while completing the study, but none were told of the study’s secret catch: all of the thermal pulses were actually the same heat level. Depending on how the participant characterized each song (from somber to upbeat to angry), they were more likely to rate a lower intensity of pain if they perceived the background music with a positive connotation [23].

Flow and Bend: How Music Enables Deep Cognition and Neuronal Activity

In fact, the context of music is so influential on the brain that each genre of music carries its own implications for the listener’s cognitive state. Neurosurgeons often prefer to play classical music for their patients, particularly by Wolfgang Amadeus Mozart. Consider Ludwig van Beethoven’s Für Elise and Mozart’s K448, two Classical-era upbeat pieces that practically drip with dynamic contrast (the musical quality of loudness and softness). One might expect that two songs with so many similarities would produce nearly identical neurological effects, but this is not the case. K448 and much of Mozart’s discography, unlike Für Elise and most Classical era pieces, contain a nested acoustic superstructure—a specialized combination of auditory frequencies outside of the normal human hearing range—that promotes theta wave activity in the hippocampus [24]. These theta waves are critical for deep cognitive processing, capable of producing a “flow state” characterized by intense concentration and focus [25].

Effectively, flow state enables neurosurgery patients to respond to intraoperative mapping tests with greater efficacy while slowing the risk of excessive brain bleeding. To better understand the nature of “flow” and its role in neurosurgery, consider a 2015 study at the Sapienza University of Rome: Subjects were presented with either K448 or Fur Elise,

and the electroencephalogram (EEG) recordings of the Mozart group indicated significantly more higher-level cognition than in the Beethoven group [26]. One theory supporting this observation concerns Brain Tissue Pulsatility (BTP), the biomechanical flow of blood to and from the brain as the heart beats. BTP is crucial for neural activity because it sets the pace of oxygen flow to the brain, and subsequently the speed of thought [27]. The slow, pulsating rhythm underlying Mozart’s more rapid pieces entrains brain activity until said rhythm matches to BTP. This meditative rhythm encourages the brain to slow overall blood flow while stimulating the prefrontal cortex, the central tenet of patient cognition [28]. This produces a dual effect of minimizing the amount of oxygen transported to the brain while maximizing the reward that the brain reaps from that incoming oxygen.

And yet, altering BTP is not music’s most profound effect on the brain. Perhaps most peculiarly, music may have the potential to induce neuroplasticity, the process of synaptic rewiring as the brain is exposed to new stimuli. In simpler terms, neuroplasticity restructures the different connections within the brain into new patterns on both a structural and a functional level. This has numerous therapeutic implications for medicine, as neuroplasticity can enable a toddler to learn complex language and motor skills or allow a traumatic brain injury (TBI) patient to partially recover from severe brain damage. In a typical patient, traumatic brain injury can sever entire networks of neural pathways. Over time, encouraging that patient to engage in higher-order cognitive activity may stimulate some regrowth of synaptic connections. Unfortunately, neuroplasticity is relatively limited in adult patients, as their capacity for neuronal growth is diminished compared to children with developing brains. Introducing music therapies to a recovering TBI patient can sponsor activity in both the auditory-motor and auditory-sensory pathways, igniting the cognitive activity that leads to neuroplasticity and accelerating the postoperative healing process [29].

The most effective way to measure this healing process is not always apparent. Consider a case study involving a professional violinist suffering from a tumor within her supplementary motor area, an area of the frontal lobe responsible for executing complex motor sequences like the precise handling of a violin and bow [30]. Concerned about the tumor’s proximity to brain tissue essential for a musical career, her surgical team opted to employ awake craniotomy procedures by monitoring her motor function, speech, language, and music recognition capabilities prior to and throughout the surgery. Before operating, she performed a complex yet familiar piece on violin (Bach’s Partita No. 2 in D minor, Allemande) so that the team could obtain a baseline record of her neuro-musical capabilities. All was proceeding as expected—then chaos struck. The patient began to seize mid-operation, abnormal electrical signals firing at random between her neurons. Grasping for information, the surgeon quickly recalled the patient’s vital records from playing Allemande and used them to estimate the patient’s specific neuroanatomy and sensitivity to auditory stimuli, projecting a timeline for how soon the seizure would end. Thanks to the investigative properties of music in awake craniotomy, the patient returned to a relaxed state and the surgery concluded without interruption.

Music: The Present and Future of Neurosurgery

Neurosurgery can be a daunting prospect for any patient, demanding meticulous attention from the surgical team. That is why musical techniques are such a flexible addition to the surgeon’s toolbox, allowing the surgeon to map the landscape of the patient’s brain, stimulate cognitive activity, and alleviate potential stress for all parties involved. Whether you plan to stand at the head of the operating table or lie on it, music has your back.

“How does this feel?” the neurosurgeon repeats. Although your eyes remain closed, you startle as the voice interrupts the waltzing harp in the background. Sinking into airy oblivion, you detect—no, not quite detect, you feel— Holtz’s melodies pour into the space where you know your spinal column to be. “Good,” you say. “I feel it.” Although your other senses are temporarily blinded, you can almost hear the smile crease your surgeon’s mask. “Perfect.”

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