219
saccule (Highstein et al. 1992; Edds-Walton 1998a). However, these data provide
further evidence that some region of the saccule could contribute to circuits that
modulate orientation with respect to gravity (yaw, pitch, roll) as well as circuits
involved in behavioral responses to sound.
3.4.3 Torus Semicircularis
As in other teleosts, the midbrain of the oyster toadfish is a major integration site of
sensory information. Visual input converges with other senses important for appropriate behavioral responses, as in other vertebrates (Tricus and Highstein 1990; Carr
and Edds-Walton 2008; Straka and Baker 2013). Multimodal cells are to be expected,
though sorting out the particular range of responses is a daunting task. The studies
by Edds-Walton and Fay focused on auditory processing and the potential for integration of hearing and components of the lateral line sense (also known as Svenning;
for a review, see Braun and Sand 2014).
The midbrain torus semicircularis of teleost fishes consists of two divisions: the
more dorsal nucleus centralis (NC) and the more ventral nucleus ventrolateralis
(NVL). Anterograde transport of neurobiotin from dDON revealed projections to
the dorsal division of the secondary octaval population (SOdor) and to the auditory
midbrain (NC). Retrograde transport of neurobiotin injected at characterized auditory sites in NC confirmed that a subset of dDON cells and SOdor cells projected to
those sites (Edds-Walton and Fay 2003). Clearly, these inputs provide a multitude
of possibilities for physiological computations in the midbrain. In addition, cells in
NC and NVL have extensive processes, and interactions between the auditory input
to NC and the lateral line input to NVL provide further opportunities for converging
the inputs from those two sensory systems. Bimodal cells with a variety of response
characteristics appear to be present in both nuclei (Fay and Edds-Walton 2001;
Edds-Walton and Fay 2005a).
Auditory cells in the midbrain lack phase-locking, are broadly tuned as in DON,
and exhibit sensitivity to temporal codes (interpulse intervals, Fay and Edds-Walton
2002). The bandwidth indicates that most cells that respond best to 100 Hz will also
respond well to harmonics of 50 Hz (the lowest frequency tested) or 200 Hz if they
are present at a similar level. Therefore, at least some of the cells in the NC respond
very well to the pulses in conspecific vocalizations.
The auditory (and bimodal) cells also exhibit sharpened DRPs; however, the data
indicated that the computations that produce sharpening continue along the ascending pathway (e.g., via SOdor) or occur in the TS. The distribution of SR values for
cells in the TS is shifted toward lower values, indicating greater sharpening, particularly in the horizontal plane, in the TS (Fig. 5c). More than half of TS cells were in
the highly sharpened category. The median SR value for azimuth among TS cells
was 0.49 (DON median SR in azimuth = 0.67) and the median SR value for elevation
among TS cells was 0.54 (DON median SR in elevation = 0.62). In addition, there
was an even greater variety in the relative sharpening of the two planes in TS (coefficient of determination = 0.1) compared to DON (coefficient of determination = 0.4),
What the Toadfish Ear Tells the Toadfish Brain About Sound
saccule (Highstein et al. 1992; Edds-Walton 1998a). However, these data provide
further evidence that some region of the saccule could contribute to circuits that
modulate orientation with respect to gravity (yaw, pitch, roll) as well as circuits
involved in behavioral responses to sound.
3.4.3 Torus Semicircularis
As in other teleosts, the midbrain of the oyster toadfish is a major integration site of
sensory information. Visual input converges with other senses important for appropriate behavioral responses, as in other vertebrates (Tricus and Highstein 1990; Carr
and Edds-Walton 2008; Straka and Baker 2013). Multimodal cells are to be expected,
though sorting out the particular range of responses is a daunting task. The studies
by Edds-Walton and Fay focused on auditory processing and the potential for integration of hearing and components of the lateral line sense (also known as Svenning;
for a review, see Braun and Sand 2014).
The midbrain torus semicircularis of teleost fishes consists of two divisions: the
more dorsal nucleus centralis (NC) and the more ventral nucleus ventrolateralis
(NVL). Anterograde transport of neurobiotin from dDON revealed projections to
the dorsal division of the secondary octaval population (SOdor) and to the auditory
midbrain (NC). Retrograde transport of neurobiotin injected at characterized auditory sites in NC confirmed that a subset of dDON cells and SOdor cells projected to
those sites (Edds-Walton and Fay 2003). Clearly, these inputs provide a multitude
of possibilities for physiological computations in the midbrain. In addition, cells in
NC and NVL have extensive processes, and interactions between the auditory input
to NC and the lateral line input to NVL provide further opportunities for converging
the inputs from those two sensory systems. Bimodal cells with a variety of response
characteristics appear to be present in both nuclei (Fay and Edds-Walton 2001;
Edds-Walton and Fay 2005a).
Auditory cells in the midbrain lack phase-locking, are broadly tuned as in DON,
and exhibit sensitivity to temporal codes (interpulse intervals, Fay and Edds-Walton
2002). The bandwidth indicates that most cells that respond best to 100 Hz will also
respond well to harmonics of 50 Hz (the lowest frequency tested) or 200 Hz if they
are present at a similar level. Therefore, at least some of the cells in the NC respond
very well to the pulses in conspecific vocalizations.
The auditory (and bimodal) cells also exhibit sharpened DRPs; however, the data
indicated that the computations that produce sharpening continue along the ascending pathway (e.g., via SOdor) or occur in the TS. The distribution of SR values for
cells in the TS is shifted toward lower values, indicating greater sharpening, particularly in the horizontal plane, in the TS (Fig. 5c). More than half of TS cells were in
the highly sharpened category. The median SR value for azimuth among TS cells
was 0.49 (DON median SR in azimuth = 0.67) and the median SR value for elevation
among TS cells was 0.54 (DON median SR in elevation = 0.62). In addition, there
was an even greater variety in the relative sharpening of the two planes in TS (coefficient of determination = 0.1) compared to DON (coefficient of determination = 0.4),
What the Toadfish Ear Tells the Toadfish Brain About Sound