Wilder Penfield’s Contributions to Auditory Science: A Commentary

Abbie White, B.S.
Au.D. Student, University of Arizona, Department of Speech, Language and Hearing Sciences

 

Wilder Graves Penfield was a neurosurgeon whose contributions were vital to the field of auditory science. Born on January 26, 1891, in Spokane, Washington, Penfield made an impact at an early age. Penfield attended Princeton University where he became a beloved classmate and football star. Penfield was awarded a scholarship to pursue graduate studies in neuropathology at Merton College, Oxford. After a term at Oxford, World War I halted his studies and Penfield worked as a medic at a Red Cross military hospital in France. Penfield was wounded in 1916. Following his time at the Red Cross, Penfield moved back to the United States, married, and started his medical degree at Johns Hopkins School of Medicine. Penfield claimed that the Red Cross hospital cultivated his love for the art of surgery and working with epileptic patients. His work on epileptic patients led to some of the first studies on human subjects to determine auditory regions in the cortex. (Costandi, 2008).

Upon completing his medical degree, Penfield studied under Harvey Cushing, the father of modern neurosurgery. One of Penfield’s first published studies developed in Spain after researching cortical scar formation following an injury. After moving to New York, Penfield began focusing on patients with epilepsy. Dr. Penfield’s work on epileptic patients led to impactful discoveries of the auditory cortex. Feeling uncertain about a successful career in New York, Penfield accepted an invitation to Montreal, Quebec where he became the city’s first neurosurgeon. Penfield and colleague Dr. William Cone established a neurosurgical unit together once they moved to Montreal. A few years later, Penfield visited a German neurosurgeon, Dr. Otfried Foerster, who introduced him to electrical stimulation of the human cortex while patients were under local anesthesia. Preceding a substantial grant from the Rockefeller Foundation, Penfield and Cone established the Montreal Neurological Institute (MNI) at McGill University. After opening in 1934, the MNI became a foundational location for teaching and practicing neurosurgery. Penfield was the director of the MNI until 1960. (Costandi, 2008). The MNI was then, and is now, a highly regarded brain research institute, which conducted considerable research on the auditory system. Doctors Kimura, Milner, and now Zattore among many others, have conducted groundbreaking auditory research there.

As director of the MNI, Penfield virtually had no limits to his work. Penfield was inspired to continue improving the procedure he learned in Germany to serve patients with epilepsy. In 1952, Penfield and colleagues created a method of surgery that allowed brain operation on epileptic patients. This surgery is known as the Montreal Procedure. The patients were awake during the operation using local anesthesia and the brain was stimulated to detect the origin of damaged cells. After detection, the patients underwent surgery to remove the impaired cells while maintaining the integrity of the surrounding healthy tissue. Penfield’s work was critical, considering he completed some of the first auditory cortex studies on humans.

It is important to note how Penfield’s intentions to improve the treatment of epilepsy led to key discoveries of the entire cortex. Previously, studies were conducted on a variety of animal species and generalized to humans. Penfield quickly discovered that stimulating specific areas on the cortex provoked perceptual experiences that the patient was able to describe. Penfield would mark a small piece of paper with a number that was placed on the cortex at the exact point where a sensation would manifest. The numbered areas with substantial auditory sensations began to line up with what we now know as the main auditory cortex areas, including the Sylvian fissure, Heschl’s gyrus, and planum temporale. Through this technique, Penfield created maps of the sensory and motor cortices of the brain and their connections to the body. The maps are known as cortical homunculus and are still used today. Moreover, Penfield’s operations led to the discovery that the body is faithfully mapped within the brain. (The Neuro, 2020).

Penfield and Perot (1963) initiated the map of the primary auditory sensory cortex along the perisylvian fissure based on patient responses. Penfield also created a map based on electrical stimulation of the superior temporal plane. This mapping determined that the core of the auditory sensory cortex was located more posteriorly within the Sylvian fissure, at Heschl’s gyrus. Additionally, some auditory responses occurred at the posterior planum temporale. Heschl’s gyrus and planum temporale are now regarded as key active auditory areas in the cortex, owing to Penfield’s research.

Penfield subsequently discovered that certain stimulation sites induced auditory hallucinations in the temporal lobe. To clarify, Penfield termed these sensations as experiential hallucinations, though present-day criteria may not define them as this. Penfield used the stimulation responses to map the visual and auditory regions of the brain. Some of Penfield’s innovative findings regarding the central auditory system can be reviewed in the journal Brain. In an earlier study by Penfield (1957), initial findings of the auditory areas were described in humans. Penfield noted that auditory areas appear to be in the transverse gyrus of Heschl. In the same 1957 study, Penfield made connections to the vestibular system based on previous animal studies. Penfield claimed, “the pathway of vestibular sensory information makes a detour from thalamus out to cortex where the vestibular area is next to the auditory area in the superior temporal convolution of both sides” (Penfield, 1957, p. 698). In 1963, Wilder Penfield and Phanor Perot summarized findings for auditory and visual experiences in several hundred patients. Immediately upon electrical stimulation along the perisylvian fissure, some patients began to express that they heard voices, music, or buzzing sounds. Although many patients did not experience these sensations, several of them did. This data was so ground-breaking that Penfield and Perot (1963) committed an entire 100-page article detailing the findings.

Ensuing hundreds of patient operations, Penfield was able to make substantial discoveries to not only the location of the auditory cortex but also discoveries of hemisphere distinctions. The patients with detectable auditory hallucinations upon stimulation would describe their experiences during the length of the stimulation. Penfield’s research revealed that auditory experiential hallucinations could be electrically stimulated in both hemispheres along the perisylvian fissure, but the types of auditory hallucinations differed between hemispheres. During left hemisphere stimulation, patients would describe auditory hallucinations involving voices, words, and mumbling. In contrast, right hemisphere stimulation generated rhythmic responses such as music, clicks, instruments, and singing. For example, one patient had a meningeal fibroblastoma removed from the left middle fossa, the growth of the tumor had pushed the temporal lobe backward. After the procedure, this patient had auditory hallucinations that consisted of voices that seemed to come from the right side. Another patient had a right temporal tumor and reported hearing a bell and seeing a woman during her seizure attacks. (Penfield & Perot, 1963).

Aside from extensive findings within the sensory and motor cortices, Penfield’s work led to early discoveries of localization and contralateral effects of sensory and motor systems. For example, Penfield’s patients would sometimes report auditory hallucinations coming from the side opposite of the stimulation. (Penfield & Perot, 1963).

Penfield had a significant influence on the field of auditory science. Seeing his exceptional contributions to surgical science, Penfield received the Lister Medal in 1960, the year he retired as director of the MNI. Penfield opened the door to stimulation during neurosurgery on humans. The Montreal Procedure is still practiced on epileptic patients today. Penfield was also one of the first researchers to operate on human cortices, which paved the way for concrete conclusions in the human species. With predominant impact to our field, Penfield termed the primary auditory cortex regions as we know them today. Penfield eventually passed away in 1976. Penfield had a lasting impact on neuroanatomy and continues to remain a foundational figure in auditory cortex findings.

 

Suggested Readings

  1. Costandi, M. (2008). Wilder penfield, neural cartographer. Neurophilosophy. Retrieved from https://neurophilosophy.wordpress.com/2008/08/27/wilder_penfield_neural_cartographer/.
  2. Penfield, W. & Perot, P. (1960). Hallucinations of past experience and experiential responses to stimulation of temporal cortex. Transactions of the American Neurological Association. 85: 80-4.
  3. Penfield, W. (1958). Functional localization in temporal and deep sylvian areas. Research Publications – Association for Research in Nervous and Mental Disease. 36: 210-26.
  4. Penfield, W. & Perot, P. (1963). The brain’s record of auditory and visual experience. a final summary and discussion. Brain, 86(4), 595–696.
  5. Penfield, W. (1957). Vestibular sensation and the cerebral cortex. The Annals of Otology, Rhinology, and Laryngology. 66(3) 691-8.
  6. Wilder Graves Penfield. (2020). The Neuro. Retrieved from https://www.mcgill.ca/neuro/about/wilder-graves-penfield.

About Pathways

Pathways is both a column that covers topics related to CAPD and Neuroaudiology and a society for people interested in central auditory disorders that regularly meets to discuss these issues.

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