BioelectricityVol. 5, No. 2 MemoriamFree AccessIn Memoriam: Lawrence B. Cohen (1939–2023)Amanda FoustAmanda FoustAddress correspondence to: Amanda Foust, PhD, Department of Bioengineering, Imperial College London, London SW7 2AZ, England E-mail Address: a.foust@imperial.ac.ukDepartment of Bioengineering, Imperial College London, London, England.Search for more papers by this authorPublished Online:16 Jun 2023https://doi.org/10.1089/bioe.2023.0020AboutSectionsPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail Larry enjoying a poster session at the 50th Anniversary of Merocyanine 540 at the scene of its discovery, the Marine Biological Laboratory (Wood's Hole, MA, August 2022). Photo courtesy of Dr. Masayuki Sakamoto.Lawrence (Larry) Baruch Cohen, pioneer of optical methods for monitoring membrane potential, died on April 19, 2023 in Providence, Rhode Island. He was born on June 18, 1939, in Indianapolis, Indiana. He graduated from University of Chicago and obtained his PhD in zoology from Columbia University. Larry was a professor at Yale University's department of cellular and molecular physiology for more than 50 years, and principal investigator of a laboratory at the Korea Institute of Science and Technology since 2012. Larry championed the development and application of optical techniques for the study of membrane potential.Larry began as a postdoctoral fellow with Richard Keynes at the world famous Physiological Laboratory (University of Cambridge, United Kingdom) studying intrinsic optical correlates of membrane function, including light scattering and birefringence. Larry's visionary perspective manifested even at this early point in his career. That is, before the requisite technology existed, Larry posited that optical methods had the potential to overcome a major hurdle to studying brain circuits with electrodes, which David Hubel likened to trying to mow the lawn with a pair of nail scissors. For the next 50 years, Larry drove the development and application of optical methods to massively parallelize the study of bioelectricity in cell physiology, biophysics, and neuroscience.From the early 1970s, Larry's laboratory, his colleagues and collaborators at Yale and the Marine Biological Laboratory (Woods Hole, MA) tested thousands of chemicals for voltage-sensitive optical contrasts, including fluorescence, absorption, and spectrum. Their efforts were soon rewarded with the discovery of Merocyanine 540's voltage sensitivity, which was great enough to enable the first single-shot optical detection of individual action potentials stimulated in a squid giant axon. Soon followed the first optical voltage recording from an intact (leech) neuron by Cohen and colleagues in 1973. In a review published the same year, Larry wrote that “it seems reasonable to imagine an array of 100 photodetectors that would allow simultaneous potential recordings from 100 individual cells.1” He pursued that vision with a determination that quickly broke ground: in 1977, Cohen's laboratory demonstrated simultaneous optical recording from 14 neurons in barnacle.2Larry continued driving the development of many more advances in optical electrophysiology over the following decades. Technologically, Larry and colleagues pursued the leading edge of molecular tools, including more and more sensitive voltage-sensitive dyes and genetically encoded indicators. In terms of hardware, Larry and his trainees adapted photodiode arrays, CCD and CMOS cameras, and image acquisition and analysis software, which they distributed through the company RedShirt Imaging. Indeed, for the past 40 years, Larry wore a red shirt almost every day, his unique style recently featured on Korean television. Scientifically, Larry's exploration spanned scales and classes from single squid axons, to invertebrate nerve cell ensembles, to olfaction in turtles and mammals.3 There has been little achieved in optical electrophysiology that does not trace its roots back to Larry's pioneering work and/or direct involvement.Larry's determination to bring to light the electrochemical interactions of 1000s of cells in parallel progressively rallied an entire community pursuing this goal. In August 2022, Larry and the international voltage imaging community celebrated the 50th anniversary of Merocyanine 540 at the scene of its discovery at Woods Hole. Despite his success and impact, Larry remained humble, generous, and warm. He led a small research group of “four or perhaps five people who worked and often lived together in harmony. On occasions when funding for salaries ran out, Larry would pay for the students' support out of his own pocket.”4 As a mentor, Larry was demanding and exceptionally devoted to the success of his trainees and collaborators, which he frequently welcomed into his home.I met Larry when I was interviewed for Yale's neuroscience doctoral program. Coming from a middle-of-wheatfields state school, I was convinced that I was out of my league. Larry bet me a dollar that I would get into Yale, but then reversed it saying that I could not bet against myself. His wall was full of dollars from bets he had won. As students, we loved attending seminars alongside Larry, who appeared to be sleeping, but at the end would, speaking slowly, ask an illuminating question. He was known for slow speech, (red) warmth, insightful and good-natured criticism, his love for culture, people, sweet wine, and jokes. His vision, dedication, and character brought together people from (at least) three continents in pursuit of optical tools to revolutionize our understanding of bioelectricity.Larry, we owe you much, thank you, and miss you.