Thalamic connections of the auditory cortex in marmoset monkeys: Core and medial belt regions

Abstract

In this study and its companion, the cortical and subcortical connections of the medial belt region of marmoset monkey auditory cortex were compared with the core region. The main objective was to document anatomical features that account for functional differences observed between areas. Injections of retrograde and bi-directional anatomical tracers targeted two core areas (A1 and R), and two medial belt areas (RM, rostromedial; CM, caudomedial). Topographically distinct patterns of connections were revealed among subdivisions of the medial geniculate complex (MGC) and multisensory thalamic nuclei, including the suprageniculate (Sg), limitans (Lim), medial pulvinar (PM), and posterior nucleus (Po). The dominant thalamic projection to CM was the anterior dorsal division (MGad) of the MGC, whereas the posterior dorsal division (MGpd) targeted RM. CM also had substantial input from multisensory nuclei, especially the magnocellular division (MGm) of the MGC. RM had weak multisensory connections. Corticotectal projections of both RM and CM targeted the dorsomedial quadrant of the inferior colliculus, while the CM projection also included a pericentral extension around the ventromedial and lateral portion of the central nucleus. Areas A1 and R were characterized by focal topographic connections within the ventral division (MGv) of the MGC, reflecting the tonotopic organization of both core areas. The results indicate that parallel subcortical pathways target the core and medial belt regions, and that RM and CM represent functionally-distinct areas within the medial belt auditory cortex.

Connections of cat auditory cortex: III. Corticocortical system

“…These areas are interconnected densely with neighboring core and belt regions, but avoid the parabelt. Their principal thalamic input is from the medial geniculate body ventral division (de la Mothe et al, 2006). In the cat, the tonotopic areas AI, AAF, P, VP, Ve are heavily interconnected, but unlike the monkey, also receive minor multisensory and limbic projections (present results).…”

“…Their principal thalamic input is from the dorsal and medial nuclei of the medial geniculate body (MGd, MGm, SG, Lim) (Hackett et al, 1998;de la Mothe et al, 2006), and these areas are heavily connected with adjacent cortical core and belt areas. The cat non-tonotopic regions (AII, DZ, AES) share many of the same types of thalamic (Lee and Winer, 2008a) and cortical connections (Fig.…”

Coding of FM sweep trains and twitter calls in area CM of marmoset auditory cortex

“…Other studies have shown that CM is tonotopically organized, and that response latencies are as short as, or shorter than, neurons in A1 (Bieser et al, 1996;Lakatos et al, 2005). A potential anatomical explanation for these features is that the principal thalamic input to CM derives from the rostral pole of the MGC, and perhaps MGv, as well (de la Mothe et al, 2006b;. In cats, neurons in the rostral pole, which has strong connections to AAF, are tonotopically organized and have short response latencies comparable to MGv (Imig et al, 1984;Imig et al, 1985;Lee et al, 2005;Lee et al, 2004;Morel et al, 1987).…”

Functional Imaging Reveals Visual Modulation of Specific Fields in Auditory Cortex

“…nar, have been shown to project to the auditory belt and parabelt areas (Fitzpatrick and Imig, 1978;Morel and Kaas, 1992;Pandya et al, 1994;Hackett et al, 1998b;de la Mothe et al, 2006) [also see Budinger et al (2006) for a study in the gerbil]. All of these structures are responsive to visual stimulation.…”