Cortical projections to the superior colliculus in prosimian galagos (Otolemur garnetti)

Abstract

The superior colliculus (SC) is a key structure within the extrageniculate pathway of visual information to cortex and is highly involved in visuomotor functions. Previous studies in anthropoid primates have shown that superficial layers of the SC receive direct inputs from various visual cortical areas such as V1, V2, and middle temporal (MT), while deeper layers receive direct inputs from visuomotor cortical areas within the posterior parietal cortex and the frontal eye fields. Very little is known, however, about the corticotectal projections in prosimian primates. In the current study we investigated the sources of cortical inputs to the SC in prosimian galagos (Otolemur garnetti) using retrograde anatomical tracers placed into the SC. The superficial layers of the SC in galagos received the majority of their inputs from early visual areas and visual areas within the MT complex. Yet, surprisingly, MT itself had relatively few corticotectal projections. Deeper layers of the SC received direct projections from visuomotor areas including the posterior parietal cortex and premotor cortex. However, relatively few corticotectal projections originated within the frontal eye fields. While prosimian galagos resemble other primates in having early visual areas project to the superficial layers of the SC, with higher visuomotor regions projecting to deeper layers, the results suggest that MT and frontal eye field projections to the SC were sparse in early primates, remained sparse in present-day prosimian primates, and became more pronounced in anthropoid primates.

Adaptive Pulvinar Circuitry Supports Visual Cognition

“…This pattern of projections has been demonstrated in a range of primates [36, 37] and other mammals such as the gray squirrel [38]. It is interesting to consider how different types of inputs might shape function at the neuronal and behavioral level.…”

Cortical projections to the superior colliculus in tree shrews (Tupaia belangeri)

“…Also, injections within the upper visual field representations of the superior colliculus resulted in labeled cells within the caudolateral half of area 18, while injections within the lower visual field representation resulted in labeled cells within the most rostromedial half of area 18, or V2 (Kaas et al, 1972). As in tree shrews, projections from occipital areas 17 and 18 have been widely reported for other mammals including rodents (Sefton et al, 1981; Olavarria and Van Sluyters, 1982; Harvey and Worthington, 1990; Rhodes et al, 1991), cats (Updyke, 1977), and various primates (Fries, 1984; Lock et al, 2003; Collins et al, 2005; Baldwin and Kaas, 2012). …”

“…Surgical procedures have been described elsewhere (Baldwin et al, 2011; Baldwin and Kaas, 2012; Wei et al, 2011). Briefly, tree shrews were initially anesthetized with an intramuscular injection of ketamine (100 mg/kg) and xylazine (6.7 mg/kg), and were maintained at anesthetic levels during surgical procedures either with isoflurane (0.5–2%) or additional supplements of ketamine and xylazine every 45 minutes.…”

“…In primates, such as New World (Cusick, 1988; Collins et al, 2005) and Old World monkeys (Fries, 1984; Lock et al, 2003), and prosimian galagos (Baldwin and Kaas, 2012), mostly visual and visuomotor areas project to the superior colliculus with visual areas projecting primarily to the superficial layers, and visuomotor areas projecting to deeper layers of the superior colliculus. Few, if any, projections arise from somatosensory areas outside of the region of S2/PV, nor do projections arise from primary motor cortex (Collins et al, 2005; Fries 1984; Baldwin et al, 2012).…”

“…Few, if any, projections arise from somatosensory areas outside of the region of S2/PV, nor do projections arise from primary motor cortex (Collins et al, 2005; Fries 1984; Baldwin et al, 2012). In contrast, in rodents such as rats and mice, the superior colliculus receives projections from primary somatosensory and motor areas of cortex, as well as from visual areas (Wise and Jones, 1977; Olavarria and Van Sluyters, 1982; Cadusseau and Roger, 1985; Welker et al, 1988; Harvey and Worthington, 1990; Hofsteter and Ehret, 1992; Inoue et al, 1992; Miyashita et al, 1994; Hoffer et al, 2005; Triplett et al, 2009; Aronoff et al, 2010).…”