246
from recordings such as AEPs that likely average the response across multiple levels
of the auditory processing pathway. In most AEP studies, what appear to be recorded
are the evoked double frequency responses of the hair cells and their afferents along
with some auditory brainstem and midbrain activity (Corwin et al. 1982 ). In contrast,
single neuron recordings can reveal specifi c fi ltering and response properties of auditory neurons. These properties include the low pass fi ltering system observed
between the hindbrain and midbrain in the Hawaiian sergeant fi sh (Maruska and
Tricas 2009b ), the sharpening of directional response properties that occurs along the
auditory pathway in the toadfi sh (Edds-Walton and Fay 2005 ), and as a generalization, the decrease in spontaneous activity, increased latency, and sharpened tuning in
the ascending auditory pathway from primary afferent to hindbrain to midbrain neurons that exists in several fi sh species (Feng and Schellart 1999 ). Thus, peripheral
and central neural recordings have uncovered many important aspects of fi sh auditory processing capabilities such as temporal encoding (Fay 1977 ; Fay and Coombs
1983 ; Carr 1986 ; Bodnar and Bass 1997 ; Kozloski and Crawford 2000 ; Bodnar et al.
2001 ), frequency selectivity, role of inhibition in shaping frequency responses, fi ltering properties, and phase-locking ability (Fay 1978a , b ; Lu and Fay 1996 ; Kawasaki
and Guo 1998 ; Sisneros and Bass 2003 ; Maruska and Tricas 2009b ), directional
sensitivity (Fay 1979 ; Lu et al. 1998 ; Edds-Walton and Fay 2003 , 2005 ), integration
with other senses (Schellart 1983 ; Prechtl et al. 1998 ; Fay and Edds-Walton 2001 ),
and effects of hormones and neuromodulators on the auditory system (Sisneros et al.
2004 ; Maruska and Tricas 2011 ).
Tuning curves from single neuron recordings, however, are diffi cult to compare
directly to techniques such as AEP and saccular potentials because the auditory
system contains neurons of many different types and response dynamics, particularly in the auditory nuclei of the brain. Thus, some individual neurons in the same
fi sh can show differences in threshold of 20–40 dB to the same frequency, be untuned, broadly tuned, or sharply tuned, be tuned to only low, mid, or high frequency
stimuli, and vary in their degree of phase-locking (Fay 1978a ; Fay and Ream 1986 ;
Lu and Fay 1993 ; Feng and Schellart 1999 ; Edds-Walton and Fay 2003 ; Maruska
and Tricas 2009b ). This individual variation may also contribute to the often lower
thresholds detected with peripheral or central single neuron recordings compared to
AEP and saccular potentials in the Hawaiian sergeant, toadfi sh, and goldfi sh (Fig. 6 ).
Further, there are also differences in temporal processing features (e.g., overall
envelope encoding, waveform structure detection) among individual neurons in the
same brain area (Fay and Coombs 1983 ; Crawford 1997 ; Bodnar and Bass 1999 ,
2001b ). These neural response characteristics are important for understanding how
fi shes encode the auditory scene and their perceptual world or “umwelt,” which
cannot be detected from behavioral, AEP, or saccular potential recordings. In fact,
single auditory neurons in the midbrain and hindbrain of the Hawaiian sergeant fi sh
are more sensitive to playbacks of natural courtship and aggressive sounds than to
single frequency tonal stimuli (Maruska and Tricas 2009b ). This indicates that
thresholds to the tonal stimuli typically used in electrophysiology recording studies
may be higher than that measured if more natural sounds which contain complex
spectral and temporal characteristics were used. Thus, single neuron recordings are
K.P. Maruska and J.A. Sisneros
from recordings such as AEPs that likely average the response across multiple levels
of the auditory processing pathway. In most AEP studies, what appear to be recorded
are the evoked double frequency responses of the hair cells and their afferents along
with some auditory brainstem and midbrain activity (Corwin et al. 1982 ). In contrast,
single neuron recordings can reveal specifi c fi ltering and response properties of auditory neurons. These properties include the low pass fi ltering system observed
between the hindbrain and midbrain in the Hawaiian sergeant fi sh (Maruska and
Tricas 2009b ), the sharpening of directional response properties that occurs along the
auditory pathway in the toadfi sh (Edds-Walton and Fay 2005 ), and as a generalization, the decrease in spontaneous activity, increased latency, and sharpened tuning in
the ascending auditory pathway from primary afferent to hindbrain to midbrain neurons that exists in several fi sh species (Feng and Schellart 1999 ). Thus, peripheral
and central neural recordings have uncovered many important aspects of fi sh auditory processing capabilities such as temporal encoding (Fay 1977 ; Fay and Coombs
1983 ; Carr 1986 ; Bodnar and Bass 1997 ; Kozloski and Crawford 2000 ; Bodnar et al.
2001 ), frequency selectivity, role of inhibition in shaping frequency responses, fi ltering properties, and phase-locking ability (Fay 1978a , b ; Lu and Fay 1996 ; Kawasaki
and Guo 1998 ; Sisneros and Bass 2003 ; Maruska and Tricas 2009b ), directional
sensitivity (Fay 1979 ; Lu et al. 1998 ; Edds-Walton and Fay 2003 , 2005 ), integration
with other senses (Schellart 1983 ; Prechtl et al. 1998 ; Fay and Edds-Walton 2001 ),
and effects of hormones and neuromodulators on the auditory system (Sisneros et al.
2004 ; Maruska and Tricas 2011 ).
Tuning curves from single neuron recordings, however, are diffi cult to compare
directly to techniques such as AEP and saccular potentials because the auditory
system contains neurons of many different types and response dynamics, particularly in the auditory nuclei of the brain. Thus, some individual neurons in the same
fi sh can show differences in threshold of 20–40 dB to the same frequency, be untuned, broadly tuned, or sharply tuned, be tuned to only low, mid, or high frequency
stimuli, and vary in their degree of phase-locking (Fay 1978a ; Fay and Ream 1986 ;
Lu and Fay 1993 ; Feng and Schellart 1999 ; Edds-Walton and Fay 2003 ; Maruska
and Tricas 2009b ). This individual variation may also contribute to the often lower
thresholds detected with peripheral or central single neuron recordings compared to
AEP and saccular potentials in the Hawaiian sergeant, toadfi sh, and goldfi sh (Fig. 6 ).
Further, there are also differences in temporal processing features (e.g., overall
envelope encoding, waveform structure detection) among individual neurons in the
same brain area (Fay and Coombs 1983 ; Crawford 1997 ; Bodnar and Bass 1999 ,
2001b ). These neural response characteristics are important for understanding how
fi shes encode the auditory scene and their perceptual world or “umwelt,” which
cannot be detected from behavioral, AEP, or saccular potential recordings. In fact,
single auditory neurons in the midbrain and hindbrain of the Hawaiian sergeant fi sh
are more sensitive to playbacks of natural courtship and aggressive sounds than to
single frequency tonal stimuli (Maruska and Tricas 2009b ). This indicates that
thresholds to the tonal stimuli typically used in electrophysiology recording studies
may be higher than that measured if more natural sounds which contain complex
spectral and temporal characteristics were used. Thus, single neuron recordings are
K.P. Maruska and J.A. Sisneros