第 1 章
Peering Into the Mind: The Revolutionary Promise of Brain Imaging
Imagine a world where your thoughts are no longer private-where scientists can watch your brain light up as you contemplate a purchase, experience fear, or tell a lie. This isn't science fiction; it's the reality of modern neuroimaging. Russell Poldrack's "The New Mind Readers" takes us on a journey through the revolutionary field of functional magnetic resonance imaging (fMRI), which has transformed neuroscience over the past three decades. The book has garnered praise from both scientific communities and mainstream publications like Scientific American for its balanced approach to a technology that promises to decode the human mind while raising profound ethical questions. As brain imaging increasingly influences fields from marketing to criminal justice, Poldrack-a Stanford professor whose own brain appears in dozens of scientific papers after he scanned himself 104 times-offers a timely exploration of what we can and cannot learn from watching the brain in action.
第 2 章
The Ultimate Scientific Challenge: Understanding Our Three-Pound Universe
The human brain presents our era's greatest scientific puzzle: how can three pounds of tissue outperform supercomputers while consuming less energy than a light bulb? This remarkable organ consumes 20% of our body's energy despite being only 2% of our body weight, processing information through networks of billions of neurons that fire in an "all-or-none" fashion. Each neuron connects to thousands of others through intricate synapses, creating a network of astronomical complexity that contains roughly 86 billion neurons and 100 trillion connections. Unlike digital computers with their modular, replaceable parts, the brain operates more like a construction team where specialists and generalists collaborate to create integrated function, with different regions seamlessly coordinating to produce consciousness, memory, and behavior.
What makes the brain fundamentally different from computers is its resilience, integration of hardware and software, and networked architecture. The story of Lisa, who regained language ability after losing an entire hemisphere to treat severe epilepsy, demonstrates this remarkable adaptability. In computers, removing half the motherboard would render the machine useless, but Lisa's remaining hemisphere reorganized itself to compensate for the loss through neuroplasticity - the brain's ability to form new neural connections and pathways. Similar cases show patients recovering from strokes, brain injuries, and even partial lobotomies, showcasing the organ's extraordinary capacity for self-repair and reorganization.
The brain's primary function is enabling adaptation to diverse environments through predictive modeling, a process neuroscientists call the "Bayesian brain." Unlike creatures adapted to specific ecological niches, humans thrive in varied conditions because our brains constantly make predictions about our environment-from assuming sidewalks will remain solid to expecting colleagues to respond in English rather than singing in Italian. These predictions operate at multiple levels simultaneously, from basic sensory processing to complex social interactions. When these predictions are violated, our brain updates its models, with dopamine neurons signaling when events exceed or fall short of expectations, creating what neuroscientists call "prediction error signals."
This prediction error coding connects to reinforcement learning, allowing us to adaptively improve our predictions over time through a sophisticated reward system. The brain maintains a delicate balance between exploring new possibilities and exploiting known solutions, regulated by neurotransmitters like dopamine, serotonin, and norepinephrine. The brain's ability to learn from experience and adjust its predictions makes it fundamentally different from traditional computers, which operate according to fixed programming rather than adapting through experience. This adaptability explains how humans can navigate novel situations with remarkable flexibility-a capability that even the most sophisticated artificial intelligence systems still struggle to match. Recent studies in computational neuroscience have revealed that this predictive processing framework may underlie everything from basic perception to complex decision-making, suggesting a unified theory of brain function.
第 3 章
From Brain to Mind: The End of Dualism
While the brain is tangible tissue that can be studied and measured, the mind's essential nature has historically been more mysterious and philosophically contentious. Rene Descartes famously proposed dualism-the influential idea that the mind exists on a separate, non-physical plane, supposedly connecting with the physical world through the pineal gland in the brain. However, modern neuroscience increasingly demonstrates that mind and brain are fundamentally inseparable, two aspects of the same underlying reality. Direct electrical stimulation of the human brain provides particularly compelling evidence for this unity, with neurosurgeons routinely implanting electrodes in epilepsy patients' brains to identify seizure origins before surgery and inadvertently triggering profound mental experiences.
When neurosurgeons stimulate specific brain regions, they can reliably evoke specific sensations, memories, or emotions-demonstrating that our subjective experiences arise directly from physical brain activity. Stimulating the temporal lobe might trigger vivid memory recall, while stimulating motor areas produces muscle movements the patient experiences as voluntary. This precise mapping between brain activity and mental experience powerfully challenges the notion that consciousness exists separately from the physical brain, suggesting instead that our thoughts, feelings, and perceptions are direct products of neural activity.
Though brain and mind are identical in substance, studying them involves different but complementary approaches. Neuroscientists study the brain directly through techniques like electrophysiology and imaging, while experimental psychologists study the mind through careful observation of behavior and experience. Roediger and Karpicke's influential memory research exemplifies psychological study-they discovered that testing oneself on material creates stronger long-term memories than simply re-reading material multiple times, though subjects paradoxically felt more confident after re-reading. Similar studies examining attention, decision-making, and emotion reveal fundamental principles of brain function without directly measuring the brain.
Before modern neuroimaging techniques, researchers relied heavily on studying patients with brain damage to understand brain function. Nineteenth-century neurologists like Paul Broca and Carl Wernicke meticulously examined stroke victims' brains post-mortem to link specific brain regions with language functions, establishing the first brain-behavior maps. More precise insights came from rare cases like patients with Urbach-Wiethe disease, which specifically damages the amygdala while sparing surrounding tissue. These patients show normal intelligence but cannot experience fear except for suffocation fear-they even laugh at stimuli that terrify most people, such as spiders, snakes, or horror movies. Such natural lesion studies remain crucial because they reveal whether brain regions are necessary for specific functions, something neuroimaging alone cannot determine.
Cognitive neuroscience represents the modern synthesis, combining both behavioral and neural approaches for a more complete understanding of mind and brain. Using techniques like functional MRI, researchers can observe neural activity while subjects perform cognitive tasks, directly linking mental processes to brain function. This integration has revolutionized our understanding of the mind-brain relationship, showing how specific neural circuits give rise to particular mental functions and experiences, from basic sensory processing to complex abstract thought. Studies of perception, memory, emotion, and consciousness increasingly reveal the neural basis of mental life, supporting a unified view of mind and brain that has largely superseded historical dualism.
第 4 章
The Birth of Functional Brain Imaging
The journey to modern brain imaging began with an unlikely nineteenth-century discovery. In 1877, Italian physician Angelo Mosso studied a man named Michele Bertino who had survived a brick falling on his head but was left with a skull hole. Mosso used this opportunity to measure brain pulsations through the opening, discovering that thinking increased brain pulsations while wrist pulse remained unchanged. This revolutionary finding suggested brain circulation responds to mental activity. Mosso further developed a "human circulation balance" that measured how the head became relatively heavier during complex mental tasks due to increased blood flow-essentially building a crude nineteenth-century brain imaging system.
A century later, positron emission tomography (PET) emerged in the 1980s as the first modern neuroimaging technique. PET works by tracking radioactive isotopes that emit positrons, which collide with electrons to produce photons. Detectors around the head capture these emissions to reconstruct where radioactive decay occurs most strongly, revealing areas of increased blood flow or glucose usage-both indicators of neural activity.
The first systematic use of neuroimaging for studying mental functions came from an unlikely collaboration between Marcus Raichle, a neurologist who helped develop PET scanning techniques, and Michael Posner, a cognitive psychologist. Their partnership bridged the sometimes uneasy relationship between psychology and neuroscience, as many scientists initially viewed the mind as too ephemeral for scientific study.
The path to fMRI began with liver researchers who discovered contrast agents caused unexpected darkening in MRI images due to effects on magnetic susceptibility. Jack Belliveau, described as "larger than life" with "boundless enthusiasm," used this insight with a new echo-planar imaging scanner to demonstrate brain function measured by MRI in 1991, showing increased signal changes in visual cortex during visual stimulation.
While Belliveau's breakthrough required injecting contrast agents with potential side effects, by late 1991, three groups raced to develop contrast-free functional MRI. Seiji Ogawa at Bell Labs had already shown in 1990 that MRI could detect blood oxygen levels, coining the term "blood oxygenation level dependent" (BOLD) contrast. At Massachusetts General Hospital, Ken Kwong successfully ran the first BOLD experiment on May 9, 1991, using Belliveau's borrowed goggles to make the visual cortex "light up." This discovery launched the modern era of functional brain imaging, allowing scientists to watch the brain in action without invasive procedures or radiation exposure.
第 5 章
Decoding the Brain's Language
Brain decoding attempts to translate between human language and the biological "language" of thought. Rather than directly "hearing" the brain speak, researchers develop a dictionary mapping between fMRI signal patterns and particular mental states. As Jack Gallant describes it, this process resembles an anthropologist creating a translation dictionary between languages by pointing at objects and recording corresponding words.
Early decoding work by John Dylan Haynes and colleagues demonstrated the ability to determine which color a person was consciously experiencing during binocular rivalry experiments. In a more striking study, Haynes showed that fMRI could predict with 70% accuracy whether participants intended to add or subtract numbers before they performed the calculation.
Jim Haxby's groundbreaking work demonstrated that fMRI could decode what a person was viewing with remarkable accuracy-over 90% across object categories and 100% for faces. To test his distributed processing hypothesis against strict localization, he showed that even after removing face-selective voxels, patterns in non-face-selective areas could still accurately identify when someone was viewing faces.
While early fMRI decoding focused on choosing between limited options, true mind reading requires reconstructing arbitrary thoughts or images from brain activity. Two groundbreaking 2008 studies moved closer to this goal by using models specifically designed to mimic the human visual system. Kendrick Kay and Jack Gallant at Berkeley tested whether they could identify natural images from a large set. After viewing almost 2,000 different images, they created a "quantitative receptive field model" that mapped which parts of the visual field each voxel in the visual cortex responded to. Testing on 120 new images, they achieved remarkable accuracy (92% for one subject, 72% for another) in identifying which image was being viewed.
Yukiyasu Kamitani's team in Kyoto took the next step by reconstructing simple viewed images, including geometric shapes and the word "neuron." Finally, Thomas Naselaris from Gallant's group achieved full natural image reconstruction by combining fMRI data with Bayesian analysis using six million internet images as prior knowledge and incorporating semantic category information.
Perhaps the most profound application of brain decoding comes from Adrian Owen's work with patients in vegetative states. Using fMRI, Owen asked individuals to imagine either playing tennis or walking through their house-tasks that produce distinctly different brain activity patterns. When testing a 23-year-old woman who had been in a vegetative state for five months following a car accident, Owen found that her brain responded appropriately to these mental imagery instructions, suggesting intact conscious awareness despite her complete unresponsiveness. This breakthrough raises profound ethical questions about whether such patients could be asked about their wishes to continue living.
第 6 章
The Neuroscience of Decision-Making
Every day we make thousands of choices ranging from inconsequential (yogurt or eggs for breakfast) to life-altering. The emerging field of neuroeconomics examines how our brains make these decisions, with neuroimaging playing a central role in this research.
Economic decisions involve weighing the value or "utility" of different prospects. While economists assume rational decision-makers always choose options with higher utility, reality proves more complex. As Daniel Bernoulli noted in the 1700s, utility decreases the more we have of something-explaining why we might pay $2 for one candy bar but not $20 for ten. This diminishing utility explains seemingly irrational choices, like preferring a guaranteed $2 million over a 50/50 chance at $10 million despite the latter's higher expected value ($5 million).
Israeli psychologists Kahneman and Tversky further demonstrated human irrationality through prospect theory, showing that losses hurt about twice as much as equivalent gains feel good ("loss aversion") and that how choices are framed significantly impacts our decisions.
Our seemingly effortless decision-making actually requires incredibly complex brain computations. In fMRI studies of gambling decisions, two brain areas show striking patterns: the ventromedial prefrontal cortex and ventral striatum both increase activity with larger potential gains but decrease activity with larger potential losses. Critically, the decrease for losses is steeper than the increase for gains-a neural signature of "loss aversion" that matches Kahneman and Tversky's prospect theory.
Reinforcement learning-learning from trial and error what's good or bad-is fundamental to survival. The neurotransmitter dopamine plays a crucial role, being released when we experience something better than expected, signaling our brain that whatever action we just took should be repeated. This learning happens through a brain circuit connecting the cerebral cortex to the basal ganglia, where dopamine strengthens connections between neurons that fire together.
Many thinkers have described human behavior as divided between rational thought and "animal spirits" or between Kahneman's impulsive "System 1" and rational "System 2." While such dichotomies oversimplify the brain's complexity, the distinction between habitual and goal-directed action has gained substantial neuroscientific support. Habits-automatic actions requiring no conscious effort-free our minds for higher-level thinking, as William James noted. But they can also override intentions, like when we drive home automatically instead of making a planned detour.
The "neural focus group" represents the holy grail for consumer neuroscience-predicting population behavior from a few individuals' brain activity. Emily Falk pioneered this approach with her groundbreaking antismoking campaign study. While subjects rated Campaign B ads most effective and standard focus groups agreed, fMRI revealed Campaign C triggered the strongest ventromedial prefrontal cortex activity. Remarkably, actual quitline call volume perfectly matched these neural predictions, not self-reported preferences.
第 7 章
Neuroimaging and Mental Illness
Mental illness takes an enormous toll on society, affecting 1 in 5 Americans annually, with 1 in 25 suffering severe functional impairment. While costing nearly $200 million yearly in lost productivity, mental health disability rates are actually rising despite massive research investment. Historically viewed as personal weakness or spiritual problems (the term "lunatic" derives from Luna, the moon goddess), mental disorders weren't considered medical conditions until the 20th century.
If mental illnesses are truly brain diseases, we should see evidence in brain imaging. Meta-analyses combining hundreds of structural MRI studies have revealed consistent patterns across different disorders. Amit Etkin's analysis of nearly 200 studies found reduced gray matter in three key regions across various disorders: the anterior cingulate cortex and both anterior insulae-areas critical for executive function and behavioral control. While some differences exist between disorders, the striking overlap suggests shared biological underpinnings despite different symptoms.
Interpreting neuroimaging studies of mental illness is complicated by confounding factors like medication effects and lifestyle differences. Antipsychotic drugs can cause gray matter decreases in most brain regions while increasing basal ganglia volume. To address these confounds, researchers study first-episode patients before medication exposure or examine unaffected first-degree relatives who share genetic risk.
The biological findings in psychiatric research have led to growing frustration with traditional diagnostic approaches, particularly the Diagnostic and Statistical Manual of Mental Disorders (DSM). The DSM defines disorders through symptom checklists-for panic disorder, patients must experience recurrent panic attacks with at least four symptoms from a list of thirteen possible manifestations. This "smorgasbord approach" means two patients with completely different symptom profiles receive identical diagnoses.
This contrasts sharply with how other medical conditions are diagnosed. Diabetes isn't diagnosed solely from symptoms like thirst or fatigue but through objective biomarkers in blood tests. Cancer treatment now relies on precise genetic profiling rather than just tumor location. This precision medicine approach-using biological knowledge to drive personalized treatment-has inspired efforts to transform psychiatric diagnosis beyond symptom checklists.
Computational psychiatry uses mathematical models to understand exactly what goes wrong in brain systems affected by mental illness. Michael J. Frank at Brown University has pioneered this approach by studying how people learn from good or bad experiences using reinforcement learning models. His work reveals how dopamine affects learning through the basal ganglia, where two neural pathways respond differently to dopamine. Applying these insights to schizophrenia, Frank found patients behaved similarly to unmedicated Parkinson's patients-impaired at learning from positive feedback but normal with negative feedback.
第 8 章
Brain Imaging in the Courtroom
When neuroimaging meets the legal system, fundamental tensions arise between science's search for general principles and the law's need for definitive judgments about individuals. While science asks whether adolescents generally have reduced impulse control, courts must determine whether a specific defendant like Christopher Simmons (who murdered Shirley Ann Crook at age 17) had diminished responsibility.
Adolescent behavior problems have been recognized since Shakespeare's time, but neuroimaging has clarified their biological basis. While the prefrontal cortex develops slowly into one's twenties, reward systems mature early and function hyperactively during adolescence. Research shows the nucleus accumbens, which receives strong dopamine input, is especially active in teenagers compared to both children and adults. This imbalance between heightened reward sensitivity and underdeveloped impulse control raises questions about criminal responsibility.
The Supreme Court has increasingly incorporated neuroscience research into landmark decisions about juvenile culpability, citing "fundamental differences between juvenile and adult minds" when striking down certain severe punishments for minors. The case of a 40-year-old man whose pedophilic behavior emerged alongside a frontal lobe tumor (and disappeared when it was removed) further complicates our understanding of brain function and moral culpability.
Criminal trials constantly require determining whether defendants are honest and witnesses accurate. Daniel Langleben pioneered fMRI lie detection while studying ADHD, theorizing that lying requires inhibiting our natural truth-telling impulse. Using a "Guilty Knowledge Test" where subjects were instructed to lie about specific playing cards, he found distinct prefrontal cortex activation during deception. Later research claimed nearly 90% accuracy in distinguishing truths from lies.
The 2009 case of Lorne Semrau, charged with Medicare fraud, became the legal test for fMRI lie detection. Cephos CEO Steven Laken scanned Semrau twice with inconsistent results, ultimately claiming his brain showed truthfulness. However, Judge Tu Pham ruled against admitting this evidence, citing small sample sizes, generalizability concerns, and lack of scientific consensus.
Philip K. Dick's "The Minority Report" imagined crime prediction through psychic powers, but real-world prediction remains statistical rather than precise. Kent Kiehl's research using mobile MRI scanners with released prisoners attempted to improve these predictions by measuring brain activity during inhibition tasks. His study found that inmates with lower activity in the anterior cingulate cortex were more likely to be rearrested. However, independent analysis showed the brain data only improved prediction accuracy by about 5%-scientifically interesting but insufficient for real-world application.
第 9 章
The Future of Mind Reading
Neuroimaging is clearly in its infancy, with our ability to decode the mind poised to become radically more powerful. Yet the translation between human language and brain language remains challenging due to the brain's complexity. FMRI combines millions of neurons into each voxel, like an intermediary summarizing countless voices. Moreover, fMRI measures blood flow changes rather than direct neural activity, with these "slow talkers" summarizing neural conversations over time.
Researchers hope stronger MRI magnets could provide better resolution. While hospital scanners typically use 1.5 tesla magnets and research centers 3 tesla, over 60 scanners worldwide now reach 7 tesla. The Netherlands houses a 9.4-tesla scanner, while Minnesota recently gained approval for a 10.5-tesla human scanner. Higher-field imaging offers not just improved spatial resolution (under one millimeter) but enables techniques more sensitive to blood oxygenation in smaller vessels closer to neural activity.
Given BOLD fMRI's fundamental limitations, researchers are exploring alternative methods to measure neuronal activity more directly. Diffusion-based fMRI attempts to detect the slight swelling of firing neurons, but signals are much smaller than BOLD and highly sensitive to head movement. Neuronal current imaging tries to measure electrical currents in firing neurons, but signals remain too small for practical application.
The reproducibility crisis in science has driven researchers to reexamine their practices, with neuroimaging being particularly susceptible due to analytical flexibility. Beyond preregistration, radical transparency through data sharing has become essential. Despite initial resistance-including a controversial 2016 editorial in the New England Journal of Medicine deriding "research parasites"-neuroimaging has emerged as a leader in data sharing.
Despite initial skepticism about how measuring blood oxygen levels could reveal brain function, fMRI has proven remarkably valuable over the past 25 years. While new concerns have emerged alongside applications to real-world questions, neuroimaging has transformed our understanding of how mental functions are organized across the brain and how different regions collaborate to enable human cognition.
We've gained insights into individual uniqueness, how brains change over different timescales, and the neural dysfunctions underlying mental illness-even driving a wholesale reconceptualization of mental disorders. Perhaps most profoundly, fMRI's ability to decode mental states raises deep questions about the mind-brain relationship and what it means for our human identity. Though every scientific technique eventually becomes obsolete, whether new technologies will surpass fMRI's capabilities within our lifetime remains uncertain-though perhaps our ventral striatum knows better than we do.
