Evoked Potentials in the Central Auditory System of Alert Porpoises to Their Own and Artificial Sounds

  • Theodore H. Bullock
  • Sam H. Ridgway


  1. 1.

    A series of 8 experiments is reported in which arrays of 7 or more electrodes on an axis were implanted stereotaxically in Tursiops truncatus. From 1 to 3 of the electrodes were in or near the inferior colliculus or lateral lemniscus.

  2. 2.

    A total of 39 electrodes out of 130 proved to be responsive to suitable acoustic stimuli. Nine of these lay above the tentorium, 30 in the midbrain above the ventral tegmentum.

  3. 3.

    The typical midbrain evoked potential is specialized for ultrasonic, ultrabrief, fast rising, closely spaced sounds like the echolocating clicks. It has a short latency and the main deflection is less than 1 ms wide. No potential is evoked if the frequency is below 5 kHz or the rise time above 5 ms.

  4. 4.

    At several cerebral loci a different response was found: long latency, long duration, slowly recovering potentials evoked by frequencies below 5 kHz whether fast or slowly rising. The cerebral “whistle” sensitive loci are probably in the posterolateral temporal cortex.

  5. 5.

    A few loci at about the tentorial level, probably rostral and lateral to the inferior colliculus gave intermediate or mixed response with some features of each of the previous 2 types.

  6. 6.

    Implanted, cooperating porpoises were trained to give series of clicks of echolocating types. These evoked potentials like those to artificial tone bursts. Often the highest intensity voluntary clicks evoked quite modest potentials and a much weaker form of click gave maximal potentials. Important differences in click composition are inferred.

  7. 7.

    Artificial echoes show more rapid recovery following the porpoise’s own click than following an artificial conditioning tone burst of equal evoking power.

  8. 8.

    It has proven practicable to place electrodes with reasonable accuracy, to combine computerized electrophysiological analysis with trained behavior and to maintain chronic implants for at least a month in porpoises. Opportunities for improvements in technique are emphasized.



Auditory System Inferior Colliculus Bottlenose Dolphin Recording Session Acoustic Pulse 
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Copyright information

© Springer Science+Business Media New York 1972

Authors and Affiliations

  • Theodore H. Bullock
    • 1
  • Sam H. Ridgway
    • 1
  1. 1.Department of Neurosciences, School of Medicine and Neurobiology Unit, Scripps Institution of OceanographyUniversity of California, San Diego and Naval Undersea Research and Development CenterSan DiegoUSA

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