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. 2012 May;295(5):800-21.
doi: 10.1002/ar.22451. Epub 2012 Mar 28.

Cortical connections of auditory cortex in marmoset monkeys: lateral belt and parabelt regions

Lisa A de la Mothe  1 , Suzanne Blumell, Yoshinao Kajikawa, Troy A Hackett
Affiliations

Cortical connections of auditory cortex in marmoset monkeys: lateral belt and parabelt regions

Lisa A de la Mothe et al. Anat Rec (Hoboken). 2012 May.

Abstract

The current working model of primate auditory cortex is constructed from a number of studies of both new and old world monkeys. It includes three levels of processing. A primary level, the core region, is surrounded both medially and laterally by a secondary belt region. A third level of processing, the parabelt region, is located lateral to the belt. The marmoset monkey (Callithrix jacchus jacchus) has become an important model system to study auditory processing, but its anatomical organization has not been fully established. In previous studies, we focused on the architecture and connections of the core and medial belt areas (de la Mothe et al., 2006a, J Comp Neurol 496:27-71; de la Mothe et al., 2006b, J Comp Neurol 496:72-96). In this study, the corticocortical connections of the lateral belt and parabelt were examined in the marmoset. Tracers were injected into both rostral and caudal portions of the lateral belt and parabelt. Both regions revealed topographic connections along the rostrocaudal axis, where caudal areas of injection had stronger connections with caudal areas, and rostral areas of injection with rostral areas. The lateral belt had strong connections with the core, belt, and parabelt, whereas the parabelt had strong connections with the belt but not the core. Label in the core from injections in the parabelt was significantly reduced or absent, consistent with the idea that the parabelt relies mainly on the belt for its cortical input. In addition, the present and previous studies indicate hierarchical principles of anatomical organization in the marmoset that are consistent with those observed in other primates.

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Figures

Figure 1
Figure 1
Schematic of the marmoset auditory cortex. (A) Lateral view of the marmoset brain with the relative location of auditory cortex. (B) Enlarged schematic of auditory cortex in the marmoset denoted by a dashed line in panel A. The lateral sulcus (LS) of the left hemisphere was graphically opened (cut) to reveal the locations of auditory cortical areas (medial belt and portions of the core region) otherwise hidden. Approximately one half-two thirds of the core region as well as the lateral belt and parabelt regions are located on the superior temporal gyrus (STG). The three regions of auditory cortex are identified with varying degrees of shading: core (dark shading), belt (light shading), parabelt (medium shading). Abbreviations: ITG, Inferior Temporal Gyrus; LS, lateral sulcus; PV, Parietoventral area; Pro, Proisocortical area; Ri, Retroinsular area; S2, Somatosensory area 2; STGr, Rostral superior temporal gyrus; STS, Superior temporal sulcus; Tpt, Temporal parietotemporal area. Scale bars: A=10mm, B=5mm.
Figure 2
Figure 2
Architecture of the marmoset auditory cortex. Low magnification images of corresponding sections of nissl, myelin, and AChE with borders drawn to identify the various regions based on respective architectonic criteria.
Figure 3
Figure 3
Ipsilateral cortical connections of areas CM/CL and CPB, case 1. Series of serial sections are arranged from caudal (upper left) to rostral (lower right), and continue onto the next page. FR labeled cells (red filled triangles) and DY labeled cells (black filled circles) are drawn onto each section, showing borders between areas identified by architectonic criteria. Black shading illustrates injection site. Dashed line in section 100 denotes where the label is artificially cut off dorsally due to interference from FR injection. Inset, schematic of marmoset auditory cortex showing location of FR injection into CM/CL, and DY into CPB.
Figure 3
Figure 3
Ipsilateral cortical connections of areas CM/CL and CPB, case 1. Series of serial sections are arranged from caudal (upper left) to rostral (lower right), and continue onto the next page. FR labeled cells (red filled triangles) and DY labeled cells (black filled circles) are drawn onto each section, showing borders between areas identified by architectonic criteria. Black shading illustrates injection site. Dashed line in section 100 denotes where the label is artificially cut off dorsally due to interference from FR injection. Inset, schematic of marmoset auditory cortex showing location of FR injection into CM/CL, and DY into CPB.
Figure 4
Figure 4
Ipsilateral cortical connections of area RTL, case 4. Series of serial sections are arranged from caudal (upper left) to rostral (lower right). FR labeled cells (filled triangles) are drawn onto each section, showing borders between areas identified by architectonic criteria. Black shading illustrates injection site. Inset, schematic of marmoset auditory cortex showing location of FR injection into RTL.
Figure 5
Figure 5
Interhemispheric cortical connections of CM/CL and CPB, case 1. Series of serial sections are arranged from caudal (upper right) to rostral (lower left). FR labeled cells (red filled triangles) and DY labeled cells (black filled circles) are drawn onto each section, showing borders between areas identified by architectonic criteria. Inset, schematic of marmoset auditory cortex showing location of FR injection in CM/CL, DY in CPB in the contralateral hemisphere.
Figure 6
Figure 6
Interhemispheric cortical connections of area RTL, case 4. Series of serial sections are arranged from caudal (upper right) to rostral (lower left). FR labeled cells (filled triangles) are drawn onto each section, showing borders between areas identified by architectonic criteria. Inset, schematic of marmoset auditory cortex showing location of FR injection in RTL in the contralateral hemisphere.
Figure 7
Figure 7
Summary of ipsilateral (left) and interhemispheric (right) connections of CM/CL. Top panels illustrate connections (arrows) of CM/CL on schematic diagram of marmoset auditory cortex. Arrow size is proportional to connection strength, as indicated in the histograms below each panel. Single arrows indicate unidirectional projections. Bottom left, white bar indicates that cell counts for ipsilateral CM/CL may be inaccurate (deflated) due to masking by the tracer injection.
Figure 8
Figure 8
Summary of ipsilateral (left) and interhemispheric (right) connections of RTL. Top panels illustrate connections (arrows) of RTL on schematic diagram of marmoset auditory cortex. Arrow size is proportional to connection strength, as indicated in the histograms below each panel. Single arrows indicate unidirectional projections. Bottom left, white bar indicates that cell counts for ipsilateral RTL may be inaccurate (deflated) due to masking by the tracer injection.
Figure 9
Figure 9
Ipsilateral cortical connections of area CPB, case 2. Series of serial sections are arranged from caudal (upper left) to rostral (lower right), and continue onto the next page. CTB labeled cells (filled triangles) are drawn onto each section, showing borders between areas identified by architectonic criteria. Black shading illustrates injection site. Inset, schematic of marmoset auditory cortex showing location of FR injection into CM/CL, and DY into CPB.
Figure 9
Figure 9
Ipsilateral cortical connections of area CPB, case 2. Series of serial sections are arranged from caudal (upper left) to rostral (lower right), and continue onto the next page. CTB labeled cells (filled triangles) are drawn onto each section, showing borders between areas identified by architectonic criteria. Black shading illustrates injection site. Inset, schematic of marmoset auditory cortex showing location of FR injection into CM/CL, and DY into CPB.
Figure 10
Figure 10
Ipsilateral cortical connections of area RPB, case 3. Series of serial sections are arranged from caudal (upper left) to rostral (lower right), and continue onto the next page. CTB-red labeled cells (filled triangles) are drawn onto each section, showing borders between areas identified by architectonic criteria. Black shading illustrates injection site. Dashed line indicates infragranular bias. Inset, schematic of marmoset auditory cortex showing location of CTB-red injection into RPB.
Figure 10
Figure 10
Ipsilateral cortical connections of area RPB, case 3. Series of serial sections are arranged from caudal (upper left) to rostral (lower right), and continue onto the next page. CTB-red labeled cells (filled triangles) are drawn onto each section, showing borders between areas identified by architectonic criteria. Black shading illustrates injection site. Dashed line indicates infragranular bias. Inset, schematic of marmoset auditory cortex showing location of CTB-red injection into RPB.
Figure 11
Figure 11
Interhemispheric cortical connections of area CPB, case 2. Series of serial sections are arranged from caudal (upper right) to rostral (lower left). CTB-red labeled cells (filled triangles) are drawn onto each section, showing borders between areas identified by architectonic criteria. Inset, schematic of marmoset auditory cortex showing location of CTB-red injection in CPB in the contralateral hemisphere.
Figure 12
Figure 12
Interhemispheric cortical connections of area RPB, case 3. Series of serial sections are arranged from caudal (upper right) to rostral (lower left). CTB-red labeled cells (filled triangles) are drawn onto each section, showing borders between areas identified by architectonic criteria. Inset, schematic of marmoset auditory cortex showing location of CTB-red injection in RPB in the contralateral hemisphere. Summary of RPB connections.
Figure 13
Figure 13
Summary of ipsilateral (left) and interhemispheric (right) connections of CPB. Top panels illustrate connections (arrows) of CPB on schematic diagram of marmoset auditory cortex. Arrow size is proportional to connection strength, as indicated in the histograms below each panel. Single arrows indicate unidirectional projections. Bottom left, white bar indicates that cell counts for ipsilateral CPB may be inaccurate (deflated) due to masking by the tracer injection.
Figure 14
Figure 14
Summary of ipsilateral (left) and interhemispheric (right) connections of RPB. Top panels illustrate connections (arrows) of RPB on schematic diagram of marmoset auditory cortex. Arrow size is proportional to connection strength, as indicated in the histograms below each panel. Single arrows indicate unidirectional projections. Bottom left, white bar indicates that cell counts for ipsilateral RPB may be inaccurate (deflated) due to masking by the tracer injection.
Figure 15
Figure 15
Image of the rostral areas from an injection of FR into RPB with the core area, R void of labeled cells creating a gap pattern.
Figure 16
Figure 16
Summary of regional connections of the lateral belt and parabelt. Dotted line denotes moderate connections from area RT of the core to the parabelt, not present in the other two core areas (A1, R). All connections between regions were found to be topographic (possible exception RM of the medial belt). Core region (dark grey), belt region (light grey), parabelt region (white). Region of injections and connectional study are denoted by thick black outline.
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