From one of several “cocktail” decks that Michael Gazzaniga has built around his house in Carpinteria, on the southern California coast, you can see the long pier at Ventura and cargo ships off in the distance and, on a clear day, the Channel Islands. As dusk settles in and glasses are refilled, the blue sky morphs into a psychedelic mix of fiery pinks and reds streaked with orange as the sun sinks, seemingly into the Pacific.

Gazzaniga has positioned the deck, reached by a staircase and a short bridge, to take advantage of a gap in the hills encircling this home away from Hanover—a rugged piece of land the world-class neuroscientist and former Dartmouth professor bought 38 years ago when it was a giant debris pile dumped by construction crews building the Ventura Freeway. Today these seven acres are covered in gardens that Gazzaniga and his wife, Charlotte, have planted through the years, including citrus groves, olive, avocado and fig trees, and nearly an acre of pinot noir grapes from which the couple bottled their first vintage last year.

It is from this hilltop Shangri-La that Gazzaniga has unleashed his latest challenge to conventional thinking about the human brain and free will. Despite an explosion of scientific evidence illuminating the interactions of billions of neurons spawned, arrayed and firing according to an individual’s genetic blueprint, Gazzaniga contends that we’re still liable for our actions.

“We are personally responsible agents and are to be held accountable for our actions, even though we live in a determined universe,” he writes in the forward of his latest book, Who’s In Charge? Free Will and the Science of the Brain. The physical brain, Gazzaniga says, simply enables our conscious minds to make choices based on what we’ve learned from experiences, relationships and the values of our social universe. Genetically determined brain function—or perceived dysfunction—should not, he contends, be the basis for legal judgments about guilt or innocence. The murderer who claims that voices in his head made him do it is still a killer and should be held accountable for his act.

Not content with a debate solely among brain scientists, Gazzaniga has taken his theory of personal responsibility into the black-and-white world of the criminal justice system to correct what he believes are faulty uses of neuroscience to excuse reprehensible behavior. His earlier work—on left- and right-brain function, memory, perception, consciousness, cognition and behavior—has already had significant impact on legal scholars, including rulings by the U.S. Supreme Court.

Gazzaniga now has his sights trained on the enormous body of case law centered on defendants’ mental competence. The questions he raises are neither easily answered nor easily dismissed. Among them: Is faulty brain circuitry a socially and legally acceptable excuse for, say, the July Colorado movie theater massacre? Gazzaniga thinks not.

“Brain determinism has no relevance to the concept of personal responsibility,” he argues in a March 18 essay in the Chronicle of Higher Education. “The exquisite machine that generates our mental life also lives in a social world and develops rules for living within a social network.…There are rules for traffic that exist and are only understood and adopted when cars interact. It is the same for human interactions. Just as we would not try to understand traffic by studying the mechanics of cars, we should not try to understand brains to understand the idea of responsibility.”

In other words, you either committed the crime or you didn’t. Neuroscience may have something to contribute to how society deals with you after a finding of guilt, but it cannot support the causal argument, “My brain made me do it.”

Gazzaniga’s bold stance doesn’t surprise longtime colleagues, nor does his decision to venture from a world in which he’s an acknowledged star into an arena where his ideas threaten the status quo. Quintessential Gazzaniga, they say. Daniel Rockmore, chair of mathematics at Dartmouth, worked with Gazzaniga on functional magnetic resonance imaging (fMRI) studies, and describes him as a “collector of ideas in every possible realm.”

Marcus Raichle, a research neurologist at Washington University School of Medicine in St. Louis and fellow member of the prestigious Institute of Medicine, agrees, noting that Gazzaniga is also someone who acts on ideas, propelling them into arenas where they have the potential to improve on established ways of doing things. “Mike has been the stimulus for so much of what neuroscience is today and someone who, as long as I’ve known him, has been thinking about how it relates to other fields,” Raichle says. “Now, whether the law likes it or not, he is thrusting neuroscience upon the adjudication process.”

Preprogrammed brain notwithstanding, Gazzaniga had no clue when he arrived at Dartmouth in 1957 that he would spend close to half a century studying interactions between biochemically driven neural networks and the social universe. At the time he was simply following the path of his older brother, Alan Gazzaniga ’58, whom he idolized.

“He was a big football star at Dartmouth and a third-string All-American. He went on to become a distinguished surgeon,” Gazzaniga says of his now-retired sibling, who lives in Tustin, California. “As soon as I set foot on the campus I loved it, loved Hanover, loved everything about my four years there.” Unlike his football- and rugby-playing brother, however, Michael refrained from going out for a team. “I was a total nerd,” he says. He did, however, join Alpha Delta and, like his brother, was also a member of Sphinx. Nerd, maybe, but that didn’t stop him from thoroughly enjoying Saturday nights at Animal House, although he opted to live in an off-campus apartment rather than in the fraternity. “It was pretty chaotic,” he recalls. “There was only so much I could take.”

Gazzaniga was part of the class of 1961’s California contingent, having grown up in the Los Angeles suburb of Glendale, where he attended the local public high school. His father was a successful surgeon and member of a visionary prepaid group practice that was a precursor to today’s Kaiser-type health plan. Gazzaniga senior expected all of his kids—Michael was the fourth of five—to go to medical school. As the son of Italian immigrants who settled in Marlboro, Massachusetts, the elder Gazzaniga was big on work ethic. Michael Gazzaniga remembers that lesson coming mostly in the form of blisters from digging postholes on a barren piece of desert that the family owned in baking-hot Indio. “Four hours each way with all of us crammed in the car every weekend,” the 6-foot-5 1/2-inch Gazzaniga recalls. “I think this was his way of making sure we didn’t get into trouble.”

At Dartmouth Gazzaniga dutifully loaded up on science courses, for which he had aptitude and interest. But his ideas about a career began to shift after he read a paper by future Nobelist Roger Sperry for a junior-year seminar taught by professor William Smith.

“It was on nerve growth and I was fascinated—so much so that I wrote Sperry to tell him I was going to be back in California over the summer and wondered if there were any jobs in his lab at Caltech for someone like me,” Gazzaniga says. “Caltech was in Pasadena and I lived in Glendale, which is only a few miles’ drive. Amazingly, he wrote back and told me about some National Science Foundation fellowships. I applied and got one.”

The experience propelled Gazzaniga into Caltech’s Ph.D. program in psychobiology immediately upon his graduation from Dartmouth. His father was baffled. Gazzaniga bemusedly recalls the conversation: “He said, ‘Why get a Ph.D. when, if you’re a doctor, you can just hire those people?’ ”

At Caltech, Gazzaniga worked with Sperry on the effects of split-brain surgery on perception, vision and other brain functions. The surgery, which was a treatment for severe epilepsy, involved severing the corpus callosum, which carries signals between the left-brain hemisphere, the seat of speech and analytical capacity, and the right-brain hemisphere, which helps recognize visual patterns. Sperry later shared the 1981 Nobel Prize in Medicine for his split-brain work with two scientists from different laboratories working on other aspects of brain research.

After receiving his doctorate from Caltech in 1964, Gazzaniga continued experimenting with split-brain patients to try to figure out why they were still managing to lead relatively normal lives with such a severe disruption in their brains’ communication architecture. Over the next 25 years he and research colleagues identified many previously unknown communication networks that these patients were able to utilize to coordinate function between the two hemispheres. These contributions helped lay the basis for current understanding not only of the complexity of neural interactions governing our conscious and unconscious life but also their role in enabling the mind to “learn” from the social world and, in turn, manage the capacity—and propensities—of the brain.

“If you look at how a complex organism works, it’s a function of layers upon layers of interaction,” Gazzaniga says. “The question for neuroscientists is ‘How do these various layers interact and coordinate themselves?’ In classic neuroscience, the rule was A fires, B reacts, C executes. In fact, A and B have a dynamic relationship. Think of a depressed person. Drug therapy can make him better and so can talk therapy, but put drug and talk therapy together and the person gets much better. What this means neuroscientifically—that this layer will [interactively] produce that layer—well, we’re still working on a vocabulary to describe it.”

Gazzaniga, whose speaking style and published writings reveal a masterful command of literary tools to communicate complex material to non-scientists, offers this metaphor: Brain = computer. Mind = software. Task = social world. In the interactions among them, the whole becomes far greater than the sum of the parts—and also intensely dynamic.

For example, a human baby can’t do much but still is driven to interact with the social world, first by gazing wide-eyed at everything her still-immature eyes can bring into focus, then by imitating the smiling face looking down at her in the crib, and later by walking, talking and exploring. Soon the neural networks responsible for processing sound and symbolic meaning figure out that a forceful “No!” means mom’s not fooling around. The toddler may not heed the emphatic command the first time. But the resulting tumble off the step will—via modules in her brain that enable humans to capture memory, feel pain and compose a narrative of what just happened—help the toddler learn to wait next time until a big person comes to hold her hand. She may still attempt the step solo, but the consequences will be hers.

“Freedom is the opportunity to acquire more information so you have more choices,” says Gazzaniga, leaping with balletic grace from neuroscience to jurisprudence. “It does not relinquish you from personal responsibility.”

Gazzaniga’s early career took him from Caltech to the University of California at Santa Barbara (UCSB), where, having come full circle, he is now professor and director of the Sage Center for the Study of the Mind. He spent only two academic years at UCSB the first time. He then went on to stints at New York University, the State University of New York at Stony Brook and Cornell University before returning in 1988 to his undergraduate stomping grounds to accept a position as professor of psychiatry at Dartmouth Medical School, where he also launched a new program in cognitive neuroscience.

Gazzaniga is widely regarded as the father of cognitive neuroscience, a field that comprises both the biological and psychological sciences and concerns itself with how the brain processes information and applies knowledge, both consciously—as in the toddler example above—and unconsciously. Examples of the latter include a body’s automatic sweating response to extreme heat or panting at the top of the stairs to replenish used-up blood oxygen or the instantaneous response of reflexive muscles when one’s hand touches a hot burner.

Raichle recalls with amusement how Gazzaniga kick-started the new field that today is so fundamental to the understanding of brain function that, says Raichle, “no respectable psychology department or brain science department exists without a cognitive neuroscience program.”

“Mike being Mike, he went to the McDonnell Foundation in St. Louis and said, ‘Hey, I’d like some money for cognitive neuroscience,’ ” Raichle says. The foundation agreed to underwrite panels of experts to define the field by culling through the relevant science about memory, motor control, perception and other key aspects of brain-mind collaboration. “Then Mike said we need a journal, so he and his wife started the Journal of Cognitive Neuroscience and ran it out of their garage. (Charlotte is still the managing editor.) Then Mike formed [in 1993] the Cognitive Neuroscience Society, which continues today.”

Gazzaniga is perhaps best known for identifying in his research with split-brain patients a left-brain module—he calls it the “interpreter” module—that gives our conscious mind the capacity to analyze actions, feelings and patterns of behavior and generates a storyline about why we do what we do or feel under certain environmental conditions. The storylines of each conscious experience converge during a lifetime of learning into a self-generated definition of who we are.

Four years after returning to Dartmouth as a professor, in 1992, Gazzaniga went back to the West for a four-year stint at the University of California at Davis, where he directed its center for neuroscience. He returned to Dartmouth in 1996, this time as the David T. McLaughlin Distinguished Professor in the College’s department of psychology and brain science. A controversial two-year stint as dean of the faculty ended in 2004 when his fellow professors “ran me out of town,” Gazzaniga says with a rueful smile of a threatened faculty revolt that briefly roiled the campus. He adds that it was a life lesson of sorts in making wiser choices about how to spend his time.

He returned in 2006 to his first employer after Caltech, UCSB. This made it possible to convert the Carpinteria house—long a vacation getaway for the Gazzanigas and their six children (including Dartmouth graduates Anne ’89 and Francesca ’07)—to a full-time home. And so ensconced, with the hills and the ocean outside his study window, Gazzaniga began his joust with the legal profession.

A forum was created by the Chicago-based John D. and Catherine T. MacArthur Foundation, which launched a law and neuroscience project in 2007 and tapped Gazzaniga to be its co-director, along with ethicist and former Dartmouth philosophy professor Walter Sinnott-Armstrong, now at Duke University. The question was how to help incorporate the latest scientific findings about the brain into law and its systems for adjudicating crime and meting out punishment.

Science has always had a role in criminal justice. TV’s popular CSI: Crime Scene Investigation franchises attest to that. The Hollywood-imagined laboratories are packed with computers and centrifuges and various other gadgets to analyze blood, hair strands, fingerprints and other bodily evidence collected at crime scenes.

The relationship of blood pressure and heart rate to truth telling, measured by lie detector machines, has been a staple of police investigations for more than a century, though not normally admissible as evidence in court.

“Science is present in all aspects of law, and neuroscience is especially important,” says Judge Jed Rakoff of the U.S. District Court for the Southern District of New York, a former federal prosecutor and white-collar crime expert who, along with brain scientists such as Raichle, was tapped to work with Gazzaniga on the MacArthur project. A verdict of guilt requires two findings, Rakoff notes: actus reus (that a criminal act was committed) and mens rea (that the act was committed by someone in a criminal state of mind). “This is what students learn in the first week of law school, so clearly mental states are a core consideration in law,” Rakoff says. “Unfortunately, the legal system has a history of being snookered by bad science.”

As neuroscience breakthroughs in the last decade claimed headlines—notably, the evidence of poor impulse control in teenagers due to still-immature brains—jurists and legal scholars struggled with how to incorporate this new science into the adjudication process. The U.S. Supreme Court took a big step in Roper v. Simmons, a 2005 case involving a 17-year-old sentenced to death for murder, striking down the death penalty for defendants age 18 and younger. In another case, an MRI scan that revealed a tumor in the part of a defendant’s brain that enables people to control their impulses helped mitigate punishment for his crime.

Another science-related ruling came previously in 1993 in Daubert et al. v. Merrell Dow Pharmaceuticals. Here, the high court targeted Gazzaniga’s pet peeve—the use of exaggerated and skewed versions of science, including much of the forensic evidence popularized by TV crime shows to sway juries. The Supreme Court ruled that trial judges must weed out junk testimony and set criteria for determining the validity of scientific testimony: So-called Daubert hearings are now a staple of federal cases that turn on scientific evidence. “I think it is fair to say that the work of Mike Gazzaniga has been behind all of these legal developments,” Rakoff says.

It would be easy for Gazzaniga, now 72, to rest on his laurels, especially in Carpinteria. He’s certainly got enough projects going on around the house to keep him busy, including a somewhat incongruous red brick walkway (New England nostalgia?) that meanders to a patio with a small metal gazebo. “I haven’t quite figured out where the path should go from there,” Gazzaniga chuckles. But bricklaying doesn’t divert him from thinking about big questions—a joy he says he discovered as an undergraduate at Dartmouth with its emphasis on the liberal arts rather than career preparation.

In a book chapter published earlier this year in the Annual Review of Psychology, Gazzaniga describes himself as someone who got hooked on science not because of a particular aptitude or theory he wanted to test but simply because of “insatiable curiosity.”

“It was all about seeing a problem that appeared sensible to me and then starting the process of thinking on your feet, that is to say, trying to solve the problem in front of you,” he writes. “It is the act of solving problems in front of us that eventually leads to larger theories about the way things work.”

Accordingly, when he left the MacArthur project in 2011—after he and Rakoff completed a slim book titled  A Judge’s Guide to Neuroscience: A Concise Introduction, to which leading scholars contributed chapters that address questions raised by judges—Gazzaniga did not stop thinking about the implications of brain science on law. Indeed, you could say that his neural networks have been worrying the subject ever since freshman year at Dartmouth when he discovered the Tower Room in Baker Library and tucked himself away to read Dostoevsky’s Crime and Punishment.

“No social organization works without the concept of responsibility, and laws express a culture’s standard of accountability,” says Gazzaniga. “The simple question, which you can answer 99 percent of the time, is, ‘Did this guy do the crime?’ The more difficult question for society is, ‘What do we do with him?’ Why we are leaving these judgments, this retributive function, in the hands of lawyers is beyond me,” Gazzaniga says. “The question should be, ‘What does the culture want to do with him?’ Neuroscience can help but only to a point, because there’s very little we can say with certainty about cause and effect in human behavior. Right now I just want to alert people that these things are bubbling up and they need to be discussed.”

It’s a discussion he enjoys having: “It’s more that I’m trying to get the conversation going than I have the answers,” he says.

Irene M. Wielawski is a freelance journalist who writes about medical science and healthcare. She is a frequent contributor to The New York Times and Health Affairs as well as DAM. She lives in Pound Ridge, New York.

CLICK HERE for an excerpt from Gazzaniga’s book, Who’s In Charge?