Celebrating 60 Years of the Readiness Potential
Have you ever stopped to consider what happens in your brain in the moments before you decide to lift your finger? This seemingly simple question led to one of the most profound discoveries in neuroscience—the Bereitschaftspotential, or readiness potential. This subtle electrical signal, which quietly prepares your brain for voluntary action, reveals that your conscious decisions are preceded by unconscious brain activity. First identified in 1964, this groundbreaking discovery challenged fundamental assumptions about free will and human consciousness 4 .
As we celebrate the 60th anniversary of this remarkable finding, scientists continue to unravel how this hidden signal shapes our understanding of the human brain.
The detection of the readiness potential opened an unprecedented window into the neural machinery of voluntary movement, transforming how neuroscientists study the relationship between brain activity and conscious intention. What began as a curious observation in a German laboratory has since blossomed into an entire field of research, illuminating the complex processes that occur before we even become aware of our own decisions.
The Bereitschaftspotential (BP), commonly known as the "readiness potential," is a slowly increasing electrical signal that emerges from the brain's motor cortex approximately 1-1.5 seconds before a person consciously decides to perform a voluntary movement.
This negative shift in electrical potential represents the brain's preparation for action—the neural equivalent of "getting ready" to move.
Prior to Kornhuber and Deecke's work, most brain research focused on the "responsive brain"—how we react to external stimuli. They found this approach unsatisfying, believing it ignored what makes us uniquely human: our capacity for self-initiated, voluntary actions 4 .
This theoretical shift was radical for its time, positioning themselves at the intersection of neuroscience and philosophy.
Think of the BP as the neural orchestra warming up before the conductor raises the baton. Just as musicians quietly tune their instruments before a performance, specific brain regions activate and synchronize their activity before you become aware of your intention to move.
"During a lunch discussion in 1964, they expressed frustration that 'the brain was investigated only as a responsive apparatus' and wondered 'what is going on in our brain before we make a voluntary movement'" 4 .
Participants sat in a Faraday cage for electrical shielding, with electrodes placed on their scalps to record brain activity through electroencephalography (EEG) 4 .
Subjects were instructed to perform simple finger flexions at irregular intervals of their own volition, without any external cues or pacing. This was crucial to ensure the movements were truly voluntary rather than responses to external stimuli 4 .
Brain electrical activity was recorded using a Schwarzer-EEG Type E 502 with tube amplifiers, while muscle activity was monitored via electromyogram (EMG). Data were stored on a Telefunken four-channel magnetic tape recorder 4 .
The key innovation was reversing the tape reels to play the recordings backward. This allowed them to average the EEG signals relative to movement onset—a technique now known as reverse averaging or opisthochronic averaging 4 .
The most significant obstacle was how to analyze brain activity before movements that occurred at unpredictable times. Traditional averaging methods required a consistent trigger preceding the event, which didn't exist for self-initiated movements. Kornhuber's ingenious solution was to use the movement itself as the trigger and look backward in time—literally by turning the tape reels around 4 .
This methodological breakthrough enabled them to see what had been invisible before: a consistent pattern of brain activity that regularly preceded voluntary movement. The researchers compared active movements with passive ones (where the experimenter moved the subject's finger), confirming that the BP only occurred before voluntary actions 4 .
Kornhuber and Deecke observed a slowly increasing ramp-up of negativity in the EEG signal that began approximately 1.5 seconds before movement onset. This negativity was stronger over the hemisphere opposite to the moving hand (contralateral dominance) and peaked at the moment of movement initiation 4 .
| Time Before Movement | Brain Activity Phase | Characteristics |
|---|---|---|
| -1.5 to -0.5 seconds | Early BP | Slow, gradual increase in negativity, bilateral distribution |
| -0.5 to 0 seconds | Late BP | Steeper increase, maximal over contralateral hemisphere |
| 0 seconds | Movement Onset | Peak negativity, followed by return to baseline |
| Hemisphere | BP Amplitude | Functional Significance |
|---|---|---|
| Contralateral (opposite to movement) | Stronger | Direct involvement in movement preparation and execution |
| Ipsilateral (same side as movement) | Weaker | Supporting role in movement coordination |
The researchers discovered that the BP was most prominent in the brain's supplementary motor area and primary motor cortex, regions now known to be crucial for movement planning and execution. The stronger contralateral activity demonstrated that the brain was specifically preparing the neural pathways needed for the upcoming movement 4 .
The BP's existence raised profound questions about free will and conscious agency. If our brain begins preparing for movement before we're consciously aware of our decision, does this mean our sense of free will is an illusion? This question became the center of intense scientific and philosophical debate, particularly following physiologist Benjamin Libet's later experiments that built upon Kornhuber and Deecke's work.
Kornhuber himself saw the BP as evidence for a positive concept of will, interpreting evolution as a process making organisms "freer and more autonomous" 4 . He believed that scientific investigation of freedom was not only possible but necessary, bridging the gap between empirical science and philosophical inquiry.
BP patterns are used in neural prosthetics to help paralyzed patients control external devices through their brain signals alone 4 .
Research has revealed altered BP patterns in patients with Parkinson's disease, Huntington's disease, and dystonia, providing insights into the pathophysiology of these conditions.
Understanding movement preparation has informed new therapeutic approaches for stroke recovery and motor rehabilitation.
Modern investigations of the BP now employ advanced technologies that Kornhuber and Deecke could only imagine:
Modern neuroscience research into phenomena like the Bereitschaftspotential relies on a sophisticated array of technical equipment and methodological approaches. While the original experiments required custom-built apparatus, contemporary labs have access to advanced technologies that continue to push the boundaries of what we can discover about voluntary movement preparation.
| Tool/Technique | Function in BP Research | Significance |
|---|---|---|
| High-Density EEG Systems | Records electrical brain activity with multiple electrodes | Allows precise localization of BP sources with millimeter accuracy |
| Concurrent fMRI-EEG | Combines temporal resolution of EEG with spatial precision of fMRI | Enables researchers to see both when and where the BP occurs |
| Transcranial Magnetic Stimulation | Temporarily disrupts or enhances specific brain areas | Tests causal relationships between brain regions and BP generation |
| Magnetoencephalography | Measures magnetic fields produced by neural activity | Provides complementary data to EEG with potentially better spatial resolution |
| Customized EMG Systems | Records muscle activation with high temporal precision | Precisely marks movement onset for accurate BP analysis |
These tools represent the evolution of neuroscience technology since the original Kornhuber and Deecke experiments. Where they used a four-channel magnetic tape recorder and manually reversed tape reels, modern researchers benefit from digital signal processing, sophisticated analysis algorithms, and multi-modal imaging approaches that continue to refine our understanding of the readiness potential.
Sixty years after its discovery, the Bereitschaftspotential continues to inspire new generations of neuroscientists. Kornhuber and Deecke's simple yet profound question—"What happens in the brain before we move?"—opened a field of research that continues to yield surprising insights about volition, consciousness, and human agency.
The BP represents one of those rare discoveries that simultaneously answers fundamental questions while raising new, more profound ones. It stands as a testament to the power of curiosity-driven science and methodological innovation.
As we celebrate this anniversary, researchers worldwide continue to build upon this foundation, using increasingly sophisticated tools to unravel the mysteries of voluntary action.
The story of the readiness potential reminds us that some of the most profound scientific discoveries often begin with simple questions about everyday experiences. The next time you deliberately raise your finger, remember that beneath that simple action lies a complex symphony of neural preparation—a hidden world of brain activity that continues to captivate scientists six decades after its initial discovery.