Long-term recognition memory of individual conspecifics is associated with telencephalic expression of Egr-1 in the electric fish Apteronotus leptorhynchus

J Comp Neurol. 2010 Jul 15;518(14):2666-92. doi: 10.1002/cne.22358.


Primates and songbirds can learn to recognize individual conspecifics based on complex sensory cues; this requires a large, highly differentiated dorsal telencephalon. Here we show that the electric fish Apteronotus leptorhynchus can learn to recognize individual conspecifics based on a simple cue, the beat frequency of their summed sinusoidal electric organ discharges (EOD). Male fish produce transient communication signals (chirps) in response to mimic EODs. The chirp response habituates over repeated stimulus presentations within one experimental session, continues to habituate over successive daily sessions and is nearly extinguished after 5-7 days. Habituation of the chirp response was specific to the presented beat frequency. The conversion of short- to long-term habituation could be disrupted by cooling the head 30 minutes after the daily habituation trials. Consolidation of long-term memory in mammals is thought to involve induced expression of an immediate early gene, Egr-1. We cloned the Apteronotid homolog of the Egr-1 gene and found that chirp-evoking stimuli induced strong expression of its mRNA within the dorsal (Dd), central (DC), and lateral (DL) subdivisions of the dorsal telencephalon. Interestingly, the dorsolateral region is hypothesized to be homologous to the amniote hippocampal formation. We conclude that A. leptorhynchus can learn to identify individual conspecifics based on their EOD frequency and can remember these frequencies for several days. We hypothesize that this form of learning, as in primates and songbirds, requires a subset of dorsal telencephalic areas and involves a consolidation-like process that includes the expression of the transcription factor AptEgr-1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cues
  • Early Growth Response Protein 1 / genetics
  • Early Growth Response Protein 1 / metabolism*
  • Electric Organ / physiology
  • Fish Proteins / genetics
  • Fish Proteins / metabolism*
  • Gymnotiformes
  • Habituation, Psychophysiologic / physiology
  • Male
  • Memory / physiology
  • Neuropsychological Tests
  • Physical Stimulation
  • RNA, Messenger / metabolism
  • Recognition, Psychology / physiology*
  • Social Behavior
  • Social Perception*
  • Telencephalon / physiology*
  • Temperature
  • Time Factors


  • Early Growth Response Protein 1
  • Fish Proteins
  • RNA, Messenger