A quantitative comparison of the hemispheric, areal, and laminar origins of sensory and motor cortical projections to the superior colliculus of the cat

Abstract

The superior colliculus (SC) is a midbrain structure central to orienting behaviors. The organization of descending projections from sensory cortices to the SC has garnered much attention; however, rarely have projections from multiple modalities been quantified and contrasted, allowing for meaningful conclusions within a single species. Here, we examine corticotectal projections from visual, auditory, somatosensory, motor, and limbic cortices via retrograde pathway tracers injected throughout the superficial and deep layers of the cat SC. As anticipated, the majority of cortical inputs to the SC originate in the visual cortex. In fact, each field implicated in visual orienting behavior makes a substantial projection. Conversely, only one area of the auditory orienting system, the auditory field of the anterior ectosylvian sulcus (fAES), and no area involved in somatosensory orienting, shows significant corticotectal inputs. Although small relative to visual inputs, the projection from the fAES is of particular interest, as it represents the only bilateral cortical input to the SC. This detailed, quantitative study allows for comparison across modalities in an animal that serves as a useful model for both auditory and visual perception. Moreover, the differences in patterns of corticotectal projections between modalities inform the ways in which orienting systems are modulated by cortical feedback. J. Comp. Neurol. 524:2623-2642, 2016. © 2016 Wiley Periodicals, Inc.

Is territorial expansion a mechanism for crossmodal plasticity?

“…(top) and are also sensitive to sound location (Clarey & Irvine, ; Korte & Rauschecker, ; Xu et al ., ; Carriere et al ., ; Las et al ., ) or sound motion (Jiang et al ., ). Functionally, the FAES is the major source of auditory corticotectal projections (Meredith & Clemo, ; Chabot et al ., ; Butler et al ., ) which is consistent with its role in SC‐mediated auditory orienting behaviors (Malhotra et al ., ; Meredith et al ., ). The FAES receives inputs largely from other ipsilateral auditory cortices, especially the AAF and the secondary auditory area (A2; Clarey & Irvine, ; Lee & Winer, ; Meredith et al ., ).…”

Cortical and thalamic connectivity to the second auditory cortex of the cat is resilient to the onset of deafness

“…In the cat, fAES is primarily responsive to auditory stimuli, but contains a subset of cells that respond to multisensory stimulation . fAES is also a major source of auditory cortical input to the superior colliculi (Meredith and Clemo 1989;Chabot et al 2013;Butler et al 2016b) and thus is expected to contribute to orienting and localization behaviours (Malhotra et al 2004;. Interestingly, A2 is considered to be part of the projections from auditory thalamus (yellow).…”

Circuits for Action and Cognition: A View from the Superior Colliculus

“…These anatomical connections of the colliculus have been discussed in many detailed reviews over the years (Borra et al 2014, Butler et al 2016, Harting 1977, Harting et al 1992, Huerta & Harting 1984, May 2006, Sparks & Hartwich-Young 1989). Worth noting, and discussed more fully below (see Figure 5), is that the ascending outputs of the motor layers of the colliculus appear denser than the descending outputs.…”