Binding by synchrony
Explanation
Wolf Singer, a German neurophysiologist at the Max Planck Institute, proposed in the 1990s an elegant solution to the "binding problem": how do the different attributes of an object processed by different neurons unify into a coherent experience? His answer: the neurons that encode attributes of the same object fire synchronously in gamma oscillations (around 40 Hz), forming a temporally bound functional assembly.
The binding problem has an everyday urgency. When you see a red car moving, the colour is processed in one brain region, the shape in another, the motion in another. No region contains the complete representation of the car. Yet you do not experience "a red", "a shape", "a motion" separately, but a red car that moves. What unites these attributes?
The hypothesis of Singer and others (Charles Gray, Andreas Engel) proposes that the solution is temporal, not spatial. Neurons coding attributes of the same object synchronize their oscillations, while those coding different objects remain desynchronized. Synchrony is the perceptual "glue" that creates units from distributed processing.
This hypothesis was supported by electrophysiological evidence: multi-electrode recordings in cat and monkey visual cortex showed that distant neurons respond synchronously in gamma when they perceive elements of the same object. Synchrony varied according to perceptual organization: two aligned lines (potentially part of the same edge) synchronized more than two separate lines.
Binding by synchrony connects with consciousness: the representations that enter global gamma synchrony are those that become conscious; those that remain desynchronized or only local do not reach conscious experience. This has been observed in experiments with perceptual tasks at the threshold of consciousness.
The hypothesis has been refined and discussed for three decades. Critics such as Andreas Engel later showed that synchrony has limitations (it is not necessary nor sufficient for consciousness, according to some studies). But brain oscillations of various frequencies (gamma, theta, alpha, beta) remain central tools for understanding perceptual integration, attention, memory and consciousness. It is a fundamental chapter of modern cognitive neuroscience.
Strengths
- Solves the binding problem elegantly.
- Empirical support in gamma synchrony recordings.
- Coherent with other oscillatory theories.
- Specific neural mechanism.
Main critiques
- Synchrony is not a sufficient condition (unconscious processes also synchronize).
- The gamma-consciousness identification is more nuanced.
- Does not address the hard problem.
- Debates about what counts as 'binding'.