Pathways for emotion: interactions of prefrontal and anterior temporal pathways in the amygdala of the rhesus monkey
Section snippets
Surgical procedures
Experiments were conducted on 26 rhesus monkeys (Macaca mulatta), obtained through the Washington and New England Regional Primate Research Centers. Experiments were conducted according to the NIH guide for the Care and Use of Laboratory Animals (NIH publication 86-23, revised 1987), and all efforts were made to minimize animal suffering and to reduce their number. The monkeys were anesthetized with ketamine hydrochloride (10–15 mg/kg, intramuscularly) followed by sodium pentobarbital
Injection sites and neural tracers
Results were obtained from experiments with injections of neural tracers in several prefrontal cortices, and in a sample of anterior temporal areas, and autonomic hypothalamic structures, both linked with the amygdala as well as with prefrontal cortices. A composite diagram of the location of tracer injections is shown in Fig. 1, and the cases, types of dyes used, injection sites and hemisphere, and analyses conducted are presented in Table 1. Details for most injection sites in prefrontal
Partly segregated input–output zones link the amygdala with orbitofrontal cortices
There is strong evidence that the amygdala and the orbitofrontal cortex have an important role in emotions (for reviews see Kling and Steklis, 1976, Aggleton, 1993, Damasio, 1994, Davis, 1997, Roberts and Wallis, 2000, Rolls, 2000, Bechara et al., 2000, Elliott et al., 2000, LeDoux, 2000). Our results indicated that the circuits connecting these structures are bidirectional, suggesting a strong functional tie. Moreover, the connections have spatially distinct input and output zones.
Conclusion
The unique role of the amygdala and the orbitofrontal cortex in emotions is not understood. The amygdala increases its activity when viewing masked fearful faces, when there is no awareness of the event (Whalen et al., 1998). Moreover, a subcortical loop connecting the amygdala with the thalamus can support fear conditioning (Romanski and LeDoux, 1992). Since the experience of emotions likely involves the cortex (Kennard, 1945), the robust bidirectional pathways linking the amygdala with
Acknowledgements
We thank Ms. Karen Trait for help with immunocytochemical assays, Dr. Ron Killiany for assistance with MR imaging, and Dr. Deepak Pandya for the autoradiographic cases. This work was supported by grants from NIH (NIMH and NINDS).
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