Eric Kandel

(1929 - )

Eric Richard Kandel is a psychiatrist, a neuroscientist and professor of biochemistry and biophysics at the Columbia University College of Physicians and Surgeons. He was a recipient of the 2000 Nobel Prize in Physiology or Medicine for his research on the physiological basis of memory storage in neurons. He shared the prize with fellow recipients Arvid Carlsson and Paul Greengard. His other honors include the National Medal of Science, the Wolf Prize, the Gairdner International Award, the Charles A. Dana Award and the Lasker Award. Kandel has been at Columbia University since 1974, and lives in New York City. Kandel has recently authored In Search of Memory: The Emergence of a New Science of Mind (WW Norton), which chronicles his life and research. The book was awarded the 2006 Los Angeles Times Book Award for Science and Technology.

Kandel was born in 1929 in Vienna, Austria, in a middle-class Jewish family. His mother had come from Kolomyya in Eastern Poland (he used to joke “as with all bright people, my roots are in Poland”) and his father from Olesko in Western Ukraine. His parents met in Vienna and married in 1923, shortly after Hermann Kandel, Eric’s father, had established a toy store. They were a thoroughly assimilated family, which had to leave Austria after the country had been invaded/annexed by Germany in March 1938, Aryanization (Arisierung) started and attacks on Jews and Jewish property escalated. Eventually Eric and his brother Ludwig, and later their parents, succeeded in moving to the U.S.

After arriving in the United States, and settling in Brooklyn, Kandel was tutored by his grandfather in Judaic studies, and was accepted at the Yeshivah of Flatbush, graduating in 1944. He attended Brooklyn's Erasmus Hall High School, a Public high school.

Kandel’s initial intellectual interests lay in the area of history, and that was his undergraduate major at Harvard University. He wrote an honors dissertation on “The Attitude Toward National Socialism of Three German Writers: Carl Zuckmayer, Hans Carossa, and Ernst Jünger.” While at Harvard, a place dominated by the work of B. F. Skinner, Kandel became interested in learning and memory. (It should be noted, however, that while Skinner championed a strict separation of psychology, as its own level of discourse, from biological considerations such as neurology, Kandel's work is essentially centered on an explication of the relationships between psychology and neurology.)

The world of neuroscience was first opened up to Kandel through his interactions with a college girlfriend, Anna Kris, whose parents were Freudian psychoanalysts. Freud, a pioneer in revealing the importance of unconscious neural processes, was at the root of Kandel's interest in the biology of motivation and unconscious and conscious memory.

Medical school and early research

In 1952 he started at the New York University Medical School. By graduation he was firmly interested in the biological basis of the mind. During this time he met his future wife, Denise Bystryn. Kandel was first exposed to research in Harry Grundfest's laboratory at Columbia University. Grundfest was known for using the oscilloscope to demonstrate that action potential conduction velocity depends on axon diameter. The researchers Kandel interacted with were contemplating the technically challenging idea of intracellular recordings of the electrical activity of the relatively small neurons of the vertebrate brain.

After starting his neurobiological work in the difficult thicket of the electrophysiology of the cerebral cortex, Kandel was impressed by the progress that had been made by Stephen Kuffler using a much more experimentally accessible system: neurons isolated from marine invertebrates. After becoming aware of Kuffler's work in 1955, Kandel graduated from medical school and learned from Stanley Crain how to make microelectrodes that could be used for intracellular recordings of relatively large crayfish giant axons.

Karl Lashley, a well known American neuropsychologist, had tried but failed to identify an anatomical locus for memory storage in the cortex at the surface of the brain. When Kandel joined the Laboratory of Neurophysiology at the National Institutes of Health in 1957, William Scoville and Brenda Milner had recently described the patient HM, who had lost explicit memory storage following removal of the hippocampus. Kandel took on the task of performing electrophysiological recordings of hippocampal pyramidal neurons. Working with Alden Spencer, electrophysiological evidence was found for action potentials in the dendritic trees of hippocampal neurons. They also noticed the spontaneous pace-maker-like activity of these neurons and a robust recurrent inhibition in the hippocampus. With respect to memory, there was nothing in the general electrophysiological properties of hippocampal neurons that suggested why the hippocampus was special for explicit memory storage.

Kandel began to realize that memory storage must rely on modifications in the synaptic connections between neurons and that the complex connectivity of the hippocampus did not provide the best system for study of the detailed function of synapses. Kandel was aware that comparative studies of behavior, such as those by Konrad Lorenz, Niko Tinbergen, and Karl von Frisch had revealed conservation of simple forms of learning across all animals. Kandel felt it would be productive to select a simple animal model that would facilitate electrophysiological analysis of the synaptic changes involved in learning and memory storage. He believed that, ultimately, the results would be found to be applicable to humans. This decision was not without risks since many senior biologists and psychologists believed that nothing useful could be learned about human memory by studying invertebrate physiology.

In 1962, after completing his residency in psychiatry, Kandel went to Paris to learn about the marine mollusk Aplysia californica from Ladislav Tauc. Kandel had realized that simple forms of learning such as habituation, sensitization, classical conditioning, and operant conditioning could readily be studied with ganglia isolated from Aplysia. “While recording the behavior of a single cell in a ganglion, one nerve axon pathway to the ganglion could be stimulated weakly electrically as a conditioned [tactile] stimulus, while another pathway was stimulated as an unconditioned [pain] stimulus, following the exact protocol used for classical conditioning with natural stimuli in intact animals.” Electrophysiological changes resulting from the combined stimuli could then be traced to specific synapses. In 1965 Kandel published his initial results, including a form of post-synaptic potentiation that seemed to correspond to a simple form of learning.

Faculty member at New York University Medical School

Kandel took a position in the Departments of Physiology and Psychiatry at the New York University Medical School, eventually forming the Division of Neurobiology and Behavior. Working with Irving Kupferman and Harold Pinsker it was possible to develop protocols for demonstrating simple forms of learning by intact Aplysia. In particular, the now famous gill-withdrawal reflex, by which the tender Aplysia gill tissue is withdrawn from danger, was shown to be sensitive to both habituation and sensitization. By 1971 Tom Carew joined the research group and helped extend the work from studies restricted to short-term memory to additional experiments that included additional physiological processes required for long-term memory.

By 1981, laboratory members including Terry Walters, Tom Abrams, and Robert Hawkins had been able to extend the Aplysia system into the study of classical conditioning, a finding which helped close the apparent gap between the simple forms of learning often associated with invertebrates and more complex types of learning more often recognized in vertebrates. Along with the fundamental behavioral studies, other work in the lab traced the neuronal circuits of sensory neurons, interneurons, and motor neurons involved in the learned behaviors. This allowed analysis of the specific synaptic connections that are modified by learning in the intact animals. The results from Kandel’s laboratory provided solid evidence for the mechanistic basis of learning as “a change in the functional effectiveness of previously existing excitatory connections.”

Molecular changes during learning

Starting in 1966 James Schwartz collaborated with Kandel on a biochemical analysis of changes in neurons associated with learning and memory storage. By this time it was known that long-term memory, unlike short-term memory, involved the synthesis of new proteins. By 1972 they had evidence that the second messenger molecule cyclic AMP (cAMP) was produced in Aplysia ganglia under conditions that cause short-term memory formation (sensitization). In 1974, the Kandel lab moved to Columbia University as founding director of the Center for Neurobiology and Behavior. It was soon found that the neurotransmitter serotonin acting to produce the second messenger cAMP is involved in the molecular basis of sensitization of the gill-withdrawal reflex. By 1980, collaboration with Paul Greengard resulted in demonstration that cAMP-dependent protein kinase (PKA) acted in this biochemical pathway in response to elevated levels of cAMP. Steven Siegelbaum identified a potassium channel that could be regulated by PKA, coupling serotonin's effects to altered synaptic electrophysiology.

In 1983 Kandel helped form the Howard Hughes Medical Research Institute at Columbia devoted to molecular neural science. The Kandel lab took on the task of identifying proteins that had to be synthesized in order to convert short-term memories into long-lasting memories. One of the nuclear targets for PKA is the transcriptional control protein CREB (cAMP response element binding protein). In collaboration with David Glanzman and Craig Bailey, CREB was identified as being a protein involved in long-term memory storage. One result of CREB activation is an increase in the number of synaptic connections. Thus, short-term memory had been linked to functional changes in existing synapses, while long-term memory was associated with a change in the number of synaptic connections.

Kandel is also well known for the textbooks he has helped write such as Principles of Neural Science. Kandel has been a member of the National Academy of Sciences, USA, since 1974. His 2006 autobiographical book, In Search of Memory: The Emergence of a New Science of Mind, is a popularized account of his life and career.

The following press release from the Royal Swedish Academy of Sciences describes Kandel’s work:

In the human brain there are more than hundred billion nerve cells. They are connected to each other through an infinitely complex network of nerve processes. The message from one nerve cell to another is transmitted through different chemical transmitters. The signal transduction takes place in special points of contact, called synapses. A nerve cell can have thousands of such contacts with other nerve cells.

The three Nobel Laureates in Physiology or Medicine have made pioneering discoveries concerning one type of signal transduction between nerve cells, referred to as slow synaptic transmission. These discoveries have been crucial for an understanding of the normal function of the brain and how disturbances in this signal transduction can give rise to neurological and psychiatric diseases. These findings have resulted in the development of new drugs.

Eric Kandel, Center for Neurobiology and Behavior, Columbia University, New York, is rewarded for his discoveries of how the efficiency of synapses can be modified, and which molecular mechanisms that take part. With the nervous system of a sea slug as experimental model he has demonstrated how changes of synaptic function are central for learning and memory. Protein phosphorylation in synapses plays an important role for the generation of a form of short term memory. For the development of a long term memory a change in protein synthesis is also required, which can lead to alterations in shape and function of the synapse.

Sea slug, a model system for learning

A phosphorylation of proteins has great importance also for the discoveries for which Eric Kandel is rewarded, that is for revealing molecular mechanisms, important for the formation of memories. Eric Kandel started to study learning and memory in mammals, but realized that the conditions were too complex to provide an understanding of basic memory processes. He therefore decided to investigate a simpler experimental model, the nervous system of a sea slug, Aplysia. It has comparatively few nerve cells (around 20.000), many of which are rather large. It has a simple protective reflex that protects the gills, which can be utilized to study basic learning mechanisms.

Eric Kandel found that certain types of stimuli resulted in an amplification of the protective reflex of the sea slug. This strengthening of the reflex could remain for days and weeks and was thus a form of learning. He could then show that learning was due to an amplification of the synapse that connects the sensory nerve cells to the nerve cells that activate the muscle groups that give rise to the protective reflex.

Short and long term memory

Eric Kandel showed initially that weaker stimuli give rise to a form of short term memory, which lasts from minutes to hours. The mechanism for this "short term memory" is that particular ion channels are affected in such a manner that more calcium ions will enter the nerve terminal. This leads to an increased amount of transmitter release at the synapse, and thereby to an amplification of the reflex. This change is due to a phosphorylation of certain ion channel proteins, that is utilizing the molecular mechanism described by Paul Greengard.

A more powerful and long lasting stimulus will result in a form of long term memory that can remain for weeks. The stronger stimulus will give rise to increased levels of the messenger molecule cAMP and thereby protein kinase A. These signals will reach the cell nucleus and cause a change in a number of proteins in the synapse. The formation of certain proteins will increase, while others will decrease. The final result is that the shape of the synapse can increase and thereby create a long lasting increase of synaptic function. In contrast to short term memory, long term memory requires that new proteins are formed. If this synthesis of new proteins is prevented, the long term memory will be blocked but not the short term memory.

Synaptic plasticity, a precondition for memory

Eric Kandel thus demonstrated that short term memory, as well as long term memory in the sea slug is located at the synapse. During the 1990's he has also carried out studies in mice. He has been able to show that the same type of long term changes of synaptic function that can be seen during learning in the sea slug also applies to mammals.

The fundamental mechanisms that Eric Kandel has revealed are also applicable to humans. Our memory can be said to be "located in the synapses" and changes in synaptic function are central, when different types of memories are formed. Even if the road towards an understanding of complex memory functions still is long, the results of Eric Kandel has provided a critical building stone. It is now possible to continue and for instance study how complex memory images are stored in our nervous system, and how it is possible to recreate the memory of earlier events. Since we now understand important aspects of the cellular and molecular mechanisms which make us remember, the possibilities to develop new types of medication to improve memory function in patients with different types of dementia may be increased.

Sources: Wikipedia, Nobelprize.org Photo courtesy Dr. Kandel