With great sadness, we announce the passing of Dr. Ehud (Udi) Kaplan, a visual neuroscientist who dedicated his life to scientific exploration. Udi died in Prague on August 17th, 2023 from idiopathic pulmonary fibrosis, an illness that affected him for the last five years of his life.
Ehud Kaplan was born in Jerusalem on December 29th, 1942. His Polish-born father, whose family was murdered during the Holocaust, was headmaster of a high school and a teacher of literature, Hebrew language and history. His mother, born in Israel, practiced as a nurse. His family cherished the value of education and integrity, as well as their Jewish heritage.
Udi was a curious boy and stood out for his intellectual qualities and excellent technical abilities. From a young age, he showed an interest in natural phenomena and biology and, alongside these interests, he was very broad-minded: well-versed in literature and poetry, the history of the Second World War, classical music – which he knew very well – and an excellent player of chess.
He served as an officer in the IDF and was a commander in a combat unit. Later, he served in the Six Day War in 1967 as a reservist.
His B.A. studies were in Psychology and Sociology at the Hebrew University in Jerusalem. During his undergraduate studies, Udi developed an interest in the physiological aspects of human behaviour and applied for a PhD in this subject at Syracuse University.
In December 1967 Udi moved from Israel to Syracuse University to become a PhD student with the visual psychophysicist Joseph F Sturr in the Department of Psychology, Syracuse University, albeit he later decided to move to the Laboratory of Sensory Communication and became a PhD student of Robert Barlow. Udi's main interest was to study brain functions and his experiments for his PhD were focused on how visual cells in the lateral eyes of the live Horseshoe crab (Limulus polyphemus) process information contained in light and also how that could be influenced by the efferent input from the Limulus brain, which contains a circadian clock. During summertime he conducted this research in the Marine Biological Laboratory (MBL), Woods Hole, MA. Later in his career he returned often to the MBL in the summer to collaborate with Bob Barlow and with Dr. Frederick Dodge (IBM Research) and others on experiments with Limulus and other marine species.
In 1972 Udi Kaplan received his PhD degree and moved to the Rockefeller University Laboratory of Biophysics to work as a postdoc with Robert (Bob) Shapley on visual processing in mammals. Udi worked in the Laboratory of Biophysics for over 20 years. At that time, he was interested in two main projects:1) transmission of visual signals from the retina to the visual cells in the Lateral Geniculate Nucleus (LGN); 2) parallel processing of contrast and color in the P and M pathways of the Macaque monkey retina and LGN. At Rockefeller, Udi worked in the lab with Shapley and many graduate students and postdocs such as Yuen Tat So, Keith Purpura, Robert Soodak, Lisa Croner, Pratik Mukherjee, Estella O’Brien, Ethan Benardete, Mavi Sanchez-Vives and Daniel Reich, among others. He was always supportive of graduate students and generous with his time in helping students to get experiments to work. He also formed lasting scientific collaborations with Professors Bruce Knight, Lawrence Sirovich (Brown University), and Jonathan Victor (Cornell University Medical School) during the years working in the Laboratory of Biophysics.
In 1995 Udi Kaplan was invited to work as tenured professor in Mt. Sinai Medical School and he continued his scientific collaboration with Professor Sirovich in their laboratory at Mt. Sinai.
As a pioneer in studying P and M cells in the monkey retina, Udi Kaplan had long been interested in the color tuning of P cells and color representation in visual cortex in general. His laboratory was one of the earliest that used intrinsic optical imaging to map various attributes including color across area V1 and V2. He threw a full support to his postdoc Youping Xiao in mapping color representation in both areas. The maps manifested themselves only when the peak locations of the responses to various colors were mapped. They were obscured when the focus was on the color tuning of individual pixels as were his preliminary results. This discovery was later confirmed by a study using 2-photon calcium imaging.
With a help of his other postdoc Marshall Crumiller, Udi start using the mathematical techniques that helped to analyze the rapidly growing technology of multi-electrode recordings. Until then, visual neuroscience was based primarily on the study of individual neurons and most of the research had focused on artificial stimuli. Professor Kaplan's team showed that neurons seem to respond more strongly to natural stimuli and developed natural stimuli as videos taken in the woods.
They used multi-electrode techniques to study the responses of multiple neurons simultaneously. By exposing groups of neurons to the same stimulus repeatedly, they were able to measure the natural variability of neurons and compare this to the range of responses to those neurons present with novel stimuli. A new mathematical technique invented by Professor Bruce Knight helped to measure the redundancy and synergy in a population of cells.
Udi was integral to this process, guiding the experiments, narrowing the parameters for the stimuli, ensuring the measurements made sense, providing context for the discoveries, and integrating the new results into the field. The seminal publication of this collaboration, Estimating the amount of information carried by a neuronal population, was released to Frontiers in Neuroscience in 2010, with a follow-up paper in 2011 that included enhancements to the methodology. In 2014 the team released a third paper to Entropy, opining on the future challenges of measuring information in large populations of neurons.
Dr. Kaplan's work has had profound implications for our understanding of the visual system. Among his many impactful publications, one of his standout pieces co-authored with Bob Shapley was titled "The primate retina contains two types of ganglion cells, with high and low contrast sensitivity." Published in the Proceedings of the National Academy of Sciences, this paper shed light on the intricate workings of the primate retina and has since become a cornerstone reference for researchers worldwide.
In April 2016 Udi and his wife Olga moved to Prague. He loved the city, it’s architecture and rich culture. He wanted to establish contact with the students and staff of Charles University, where Albert Einstein himself used to work. He made a contact with the head of the department of history and philosophy of science, Karel Kleisner and his colleague Jaroslav Flegr. Udi's erudition in neurobiology, sensory physiology, perception, and related areas seamlessly aligned with their scientific interests. Soon after their meeting Udi was appointed as a visiting professor at the Faculty of Science of Charles University in Prague. He provided consultations on various topics to the students, which help many of them successfully defend their PhDs and later actively pursuie their own scientific research. These consultations covered a wide range of phenomena, from the study of the functional architecture of the mammalian cortex to exploring the source and role of noise and fluctuations in the brain, investigating visual characteristics of invertebrates, and applying artificial intelligence and computational approaches in neuroscience.
Udi regularly participated in the Seminars in Theoretical Biology at Charles University and delivered several talks. In March 2018 he gave a talk that shows how his curious brilliant mind was constantly looking for answers on provocative questions. The title was “Is the brain stochastic, deterministic, chaotic, or just practically unpredictable?”
He will be deeply missed by students and members of the Faculty of Science of Charles University, as well as by his colleagues and students at Rockefeller University and Mt. Sinai Medical school.
Professor Kaplan is survived by his wife Olga Kaplan, two daughters from the previous marriage Liat and Alisa Kaplan and two brothers Aharon and Haim Kaplan.