Dorsal periaqueductal gray-amygdala pathway conveys both innate and learned fear responses in rats

Eun Joo Kim, Omer Horovitz, Blake A. Pellman, Lancy Mimi Tan, Qiuling Li, Gal Richter-Levin, Jeansok J. Kim

Research output: Contribution to journalArticlepeer-review


The periaqueductal gray (PAG) and amygdala are known to be important for defensive responses, and many contemporary fear-conditioning models present the PAG as downstream of the amygdala, directing the appropriate behavior (i.e., freezing or fleeing). However, empirical studies of this circuitry are inconsistent and warrant further examination. Hence, the present study investigated the functional relationship between the PAG and amygdala in two different settings, fear conditioning and naturalistic foraging, in rats. In fear conditioning, electrical stimulation of the dorsal PAG (dPAG) produced unconditional responses (URs) composed of brief activity bursts followed by freezing and 22-kHz ultrasonic vocalization. In contrast, stimulation of ventral PAG and the basolateral amygdalar complex (BLA) evoked freezing and/or ultrasonic vocalization. Whereas dPAG stimulation served as an effective unconditional stimulus for fear conditioning to tone and context conditional stimuli, neither ventral PAG nor BLA stimulation supported fear conditioning. The conditioning effect of dPAG, however, was abolished by inactivation of the BLA. In a foraging task, dPAG and BLA stimulation evoked only fleeing toward the nest. Amygdalar lesion/inactivation blocked the UR of dPAG stimulation, but dPAG lesions did not block the UR of BLA stimulation. Furthermore, in vivo recordings demonstrated that electrical priming of the dPAG can modulate plasticity of subiculum- BLA synapses, providing additional evidence that the amygdala is downstream of the dPAG. These results suggest that the dPAG conveys unconditional stimulus information to the BLA, which directs both innate and learned fear responses, and that brain stimulation-evoked behaviors are modulated by context.

Original languageEnglish
Pages (from-to)14795-14800
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number36
StatePublished - 3 Sep 2013


  • Fear circuitry
  • Learning and memory
  • Long-term depression
  • Long-term potentiation
  • Synaptic plasticity

ASJC Scopus subject areas

  • General


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