Chasing “fear memories” to the cerebellum

The cerebellum has long been known as a center of fine motor control and sensory-motor integration. It also is appreciated as essential for the acquisition and expression of conditioned eye-blink responses, a type of discrete sensory-motor learning (1, 2). Recently, the cerebellum also has been implicated in acquiring (3–5) and expressing (6) “emotional” associative learning, which is commonly believed to depend entirely on forebrain regions. Specifically, the learning and memories for an association between neutral and fear-eliciting stimuli, also known as “fear conditioning”, often are said to reside in the basolateral amygdala (ref. 7, for an alternative view see ref. 8). An elegant study by Sacchetti and colleagues in this issue of PNAS (9) adds a new dimension to the recently described role of the cerebellum in emotional learning and memory by revealing that the cerebellum is essential for consolidating memories for both tone and contextual fear conditioning for several days longer than the basolateral amygdala. Thus, their findings are not only relevant to the current debate regarding the sites of permanent storage of fear memories, but more importantly, they expand our knowledge of the topographical and chronological composition of the brain network(s) responsible for consolidating this type of memory.

The term “fear memory” typically is used to describe the plasticity in the brain underlying the long-lasting modifications in the behavior of animals that had undergone fear conditioning. Fear conditioning is a long-lasting (10) form of classical (Pavlovian) conditioning where animals learn to associate a nonfear eliciting stimulus, a conditional stimulus (CS), with an aversive stimulus, an unconditional stimulus (US), that generates a fear state expressed by a …