extended period, during which there are no significant morphological changes.
In this presentation, I’ll lead you through a set of experiments conducted at Erez Braun's lab (Technion) and the parallel development of a field-theoretic framework that explains the primary morphological transition
observed during Hydra regeneration. I will demonstrate that this morphological change can be understood
as a first-order-like phase transition characterized by an activation process over a barrier, wherein noise
plays an essential role.
I'll start with a brief look back at the history of Hydra regeneration, then move on to Braun's key finding:
exposing a Hydra’s tissue to an electric field can halt and even reverse the regeneration processes. Next, I'll
discuss experiments where we looked at the calcium ions' activity within the tissue and show that the
statistical characteristics of the calcium field can be understood as equilibrium-like fluctuations of a bistable
field.
Moving forward, I'll couple the calcium field to the tissue's Gaussian curvature and introduce the
morphological potential that dictates the probability density of the tissue's various morphological states.
Calculation of this potential yields a tilted double-well potential, where one minimum corresponds to a
spherical shape and the other to an elongated tube-like structure. The natural progression of this potential
gradually alters its tilt until the second minimum becomes the global one. It implies that the primary
morphological transition should be a first-order-like phase transition. I’ll present several experiments that
support this prediction.
To further validate this theoretical model, I'll demonstrate that by slowing down the natural evolution of
the morphological potential, the system can enter a new phase characterized by stochastic morphological
swings (see Figure below). Finally, I'll show that the system's response to a periodic shaking of the
morphological potential reflects the characteristics of a stochastic resonance with the implication that noise
plays a dominant role in Hydra morphogenesis.