Potentiation of amygdaloid and hippocampal auditory-evoked potentials in a discriminatory fear-conditioning task in mice as a function of tone pattern and context

Eur J Neurosci. 2003 Aug;18(3):639-50. doi: 10.1046/j.1460-9568.2003.02758.x.


According to the local memory storage hypothesis, information about the tone-shock association in an auditory fear-conditioning paradigm is stored in synapses within the lateral amygdala. Thus, fear-conditioning-induced potentiation of auditory-evoked potentials in response to a conditioned stimulus (CS+, a series of short lasting tones; patterned tone) has been interpreted as an in vivo correlate of amygdaloid synaptic plasticity. Here, we re-examine the specificity of potentiation of auditory-evoked potentials in terms of (i) local confinement to the lateral amygdala, (ii) parameters of CS+ and (iii) influence of context, using a discriminatory fear-conditioning paradigm. Adult male C57BL/6J mice were implanted with recording electrodes aimed at the lateral amygdala, the CA1 region of the hippocampus and the neck muscles for simultaneous recordings of auditory-evoked potentials and startle responses. In a neutral context, auditory-evoked potentials within lateral amygdala and CA1 as well as startle and freezing responses to the CS+ were significantly potentiated following conditioning, as compared with pre-conditioning values and responses to a neutral stimulus (CSn; tone of different frequency). Potentiation was only evident if CS+ was presented as a uniform series but not if presented mixed with CSn. Accordingly, mice failed to show intensified freezing to a patterned tone if a single lasting tone of the same frequency served as CS+. Both CA1 and lateral amygdala auditory-evoked potentials were potentiated in response to CSn if presented in the conditioning context. These findings demonstrate that (i) potentiation of auditory-evoked potentials is not restricted to the lateral amygdala, (ii) both tone frequency and pattern of tone presentation are essential for proper CS+ recognition and (iii) contextual memory leads to a general potentiation of auditory-evoked potentials.

MeSH terms

  • Acoustic Stimulation / methods
  • Amygdala / physiology*
  • Animals
  • Behavior, Animal / physiology
  • Conditioning, Psychological / physiology*
  • Discrimination, Psychological*
  • Evoked Potentials, Auditory / physiology*
  • Fear*
  • Hippocampus / physiology*
  • Male
  • Mice
  • Mice, Inbred C57BL