Grounding autonomous behavior in the nervous system is a fundamental challenge for neuroscience. In particular, self-organized behavioral development provides more questions than answers. Are there special functional units for curiosity, motivation, and creativity? This paper argues that these features can be grounded in synaptic plasticity itself, without requiring any higher-level constructs. We propose differential extrinsic plasticity (DEP) as a new synaptic rule for self-learning systems and apply it to a number of complex robotic systems as a test case. Without specifying any purpose or goal, seemingly purposeful and adaptive rhythmic behavior is developed, displaying a certain level of sensorimotor intelligence. These surprising results require no systemspecific modifications of the DEP rule. They rather arise from the underlying mechanism of spontaneous symmetry breaking, which is due to the tight brain body environment coupling. The new synaptic rule is biologically plausible and would be an interesting target for neurobiological investigation. We also argue that this neuronal mechanism may have been a catalyst in natural evolution.R esearch in neuroscience produces an understanding of the brain on many different levels. At the smallest scale, there is enormous progress in understanding mechanisms of neural signal transmission and processing (1-4). At the other end, neuroimaging and related techniques enable the creation of a global understanding of the brain's functional organization (5, 6). However, a gap remains in binding these results together, which leaves open the question of how all these complex mechanisms interact (7-9). This paper advocates for the role of self-organization in bridging this gap. We focus on the functionality of neural circuits acquired during individual development by processes of self-organizationmaking complex global behavior emerge from simple local rules. Donald Hebb's formula "cells that fire together wire together" (10) may be seen as an early example of such a simple local rule which has proven successful in building associative memories and perceptual functions (11,12). However, Hebb's law and its successors like BCM (13) and STDP (14, 15) are restricted to scenarios where the learning is driven passively by an externally generated data stream. However, from the perspective of an autonomous agent, sensory input is mainly determined by its own actions. The challenge of behavioral self-organization requires a new kind of learning that bootstraps novel behavior out of the self-generated past experiences. This paper introduces a rule which may be expressed as "chaining together what changes together." This rule takes into account temporal structure and establishes contact to the external world by directly relating the behavioral level to the synaptic dynamics. These features together provide a mechanism for bootstrapping behavioral patterns from scratch.This synaptic mechanism is neurobiologically plausible and raises the question of whether it is present in living beings...