Acoustically evoked potentials in two cephalopods inferred using the auditory brainstem response (ABR) approach Marian Y. Hu a , Hong Young Yan b, ⁎, Wen-Sung Chung b , Jen-Chieh Shiao c , Pung-Pung Hwang b a Institute of Marine Sciences, IFM-GEOMAR, 24105 Kiel, Germany b Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei,11529 Taiwan c Institute of Oceanography, College of Science, National Taiwan University, Taipei,10617 Taiwan abstract article info Article history: Received 12 January 2009 Received in revised form 21 February 2009 Accepted 22 February 2009 Available online 9 March 2009 Keywords: Hearing Lateral line Octopus Sound reception Squid Statocyst It is still a matter of debate whether cephalopods can detect sound frequencies above 400 Hz. So far there is no proof for the detection of underwater sound above 400 Hz via a physiological approach. The controversy of whether cephalopods have a sound detection ability above 400 Hz was tested using the auditory brainstem response (ABR) approach, which has been successfully applied in fish, crustaceans, amphibians, reptiles and birds. Using ABR we found that auditory evoked potentials can be obtained in the frequency range 400 to 1500 Hz (Sepiotheutis lessoniana) and 400 to 1000 Hz (Octopus vulgaris), respectively. The thresholds of S. lessoniana were generally lower than those of O. vulgaris. © 2009 Elsevier Inc. All rights reserved. 1. Introduction It has been speculated for more than a century, whether cephalopods can hear. Baglioni (1910) observed that blind Octopus vulgaris responded to water movements and low frequency vibrations by behavioural changes. Fifty years later, Wells and Wells (1956) reported that blind octopus could locate the direction of a sound source which was produced by tapping on the tank. Sepia officinalis responded to a stimulus of 180 Hz by changing its colour (Dijkgraaf, 1961) and Maniwa (1976) convincingly demonstrated that the squid Todarodes pacificus could be attracted by a pure tone sound of 600 Hz which was emitted from commercial squid fishing boats. An electrophysiological approach was used by Budelmann and Bleck- mann (1988) to demonstrate the detection of water vibrations ranging from 3.5 Hz to 200 Hz by the epidermal head lines of juvenile specimens of the cuttlefish S. officinalis, but response to higher frequencies (indicating possible underwater audition), were not observed. Sound perception among cephalopods has been a controversial issue since the early 20th century, due ostensibly to debate regarding the definition of hearing in an aquatic environment. As most cephalopods lack gas filled chambers, such as a swim bladder and, thus, most likely cannot detect the pressure wave component of sound. However, like fish, cephalopods (Young, 1989) and shrimp (Lovell et al., 2005) have statocysts (otoliths) that in principle can be used to detect whole body motions such as those caused by the displacement component of a sound wave. Young (1960) pointed out that the statocyst might serve as a detector for vibrations, or sound, in a similar way as the vertebrate vestibular system. The cephalopod statocyst with its macula–statolith system shows many comparative features similar to the fish inner ear with the macula–otolith complex. It is well accepted that fish (Webster et al., 1992; Kenyon et al., 1998; Yan, 1998; Fay and Popper, 1999; Yan and Curtsinger, 2000; Simpson et al., 2005) and shrimp (Lovell et al., 2005) have the ability to detect acoustic underwater stimuli of a wide frequency range using either their inner ear (in fish) or statocyst (in shrimp). In these examinations the auditory brainstem response (ABR), an electrophysiological far-field recording method that was originally used in clinical evaluation of the patients' hearing ability (Hall, 1992), had been applied. The ABR technique has never been used on cephalopod species, as these animals have no real brainstem. However, they show the presence of afferents in the statocyst and existence of neural pathway terminating in the brain, indicating that the physiology of cephalopods is suitable for the recording of acoustically evoked potentials (AEPs) with the use of ABR (Williamson and Budelmann, 1985; Hanlon and Messenger, 1996). In a study on European prawn Palaemon serratus, the ABR technique had clearly demonstrated hearing ability via the statocysts ranging from 100 Hz to 3000 Hz by this invertebrate (Lovell et al., 2005). The results of this study prompted us to formulate a hypothesis that cephalopod may also detect sound stimuli with frequencies higher than 400 Hz. Comparative Biochemistry and Physiology, Part A 153 (2009) 278–283 ⁎ Corresponding author. Tel.: +886 3 9880544; fax: +886 3 9871035. E-mail address: hyyan@gate.sinica.edu.tw (H.Y. Yan). 1095-6433/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.cbpa.2009.02.040 Contents lists available at ScienceDirect Comparative Biochemistry and Physiology, Part A journal homepage: www.elsevier.com/locate/cbpa