Visual- and saccade-related signals in the primate inferior colliculus

Abstract

The inferior colliculus (IC) is normally thought of as a predominantly auditory structure because of its early position in the ascending auditory pathway just before the auditory thalamus. Here, we show that a majority of IC neurons (64% of 180 neurons) in awake monkeys carry visual-and/or saccade-related signals in addition to their auditory responses (P < 0.05). The response patterns involve primarily excitatory visual responses, but also increased activity time-locked to the saccade, slow rises in activity time-locked to the onset of the visual stimulus, and inhibitory responses. The presence of these visual-related signals suggests that the IC plays a role in integrating visual and auditory information. More broadly, our results show that interactions between sensory pathways can occur at very early points in sensory processing streams, which implies that multisensory integration may be a low-level rather than an exclusively high-level process.auditory ͉ monkey ͉ multisensory ͉ vision ͉ cross-modal

A Rate Code for Sound Azimuth in Monkey Auditory Cortex: Implications for Human Neuroimaging Studies

“…The reason for this design is that changes in eye position can produce changes in activity in auditory cortical neurons (Werner-Reiss et al, 2003;Fu et al, 2004;Woods et al, 2006). At the same time, visual stimuli can themselves influence the responses of auditory cortical neurons (Ghazanfar et al, 2005) as well as neurons in other areas of the auditory pathway (Porter et al, 2007). Thus, it will be of interest to investigate further whether the presence of a visual stimulus alters spatial sensitivity of auditory cortical neurons, above and beyond any associated effect of eye position.…”

Systematic mapping of the monkey inferior colliculus reveals enhanced low frequency sound representation

“…C: magnified view of the square in B. Image shown in B and C has been published previously (Porter et al 2006). physiological normality and vice versa.…”

“…After recovery, an additional surgery was performed to make a craniotomy and to implant a recording cylinder positioned over the left IC. The cylinder was oriented to allow electrodes to approach the IC at an angle ϳ30°from vertical in the coronal plane, i.e., proceeding from dorsolateral to ventromedial (Groh et al 2003;Porter et al 2007). For simplicity and convenience, we will usually refer to the affected dimensions as lateral/medial and dorsal/ventral (or above/below), despite their tilt (i.e., in the axis defined by the recording chamber).…”

“…Macaques provide an excellent model for human hearing, as both humans and macaques rely greatly on audition for communication and the frequency ranges heavily overlap: ϳ30 Hz to 30 kHz for monkeys (Pfingst et al 1975;Pfingst et al 1978;Stebbins et al 1966) and 20 Hz to 20 kHz for humans (Moore 2008). Studies in monkeys also offer advantages not directly related to audition: monkeys are readily trained, and phenomena such as eye movements that cannot be studied in other mammals can be studied in monkeys [e.g., Groh et al (2001); Porter et al (2006); Zwiers et al (2004)]. Functional maps are essential to guide this work.…”

Distribution of eye position information in the monkey inferior colliculus

“…Despite occupying a pivotal position in the ascending auditory system, IC neurons are modulated by more than just acoustic stimuli. Several nonauditory factors such as visual stimuli, tactile stimuli, the position of the eyes, and impending reward also have a role in shaping neural activity (Aitkin et al 1981;Bergan and Knudsen 2009;Groh et al 2001;Gutfreund et al 2002;Mascetti and Strozzi 1988;Metzger et al 2006;Porter et al 2006Porter et al , 2007Zwiers et al 2004).…”