Evidence for "direct" and "indirect" pathways through the song system basal ganglia.
Song learning in oscine birds relies on a circuit known as the "anterior forebrain pathway," which includes a specialized region of the avian basal ganglia. This region, area X, is embedded within a telencephalic structure considered homologous to the striatum, the input structure of the mammalian basal ganglia. Area X has many features in common with the mammalian striatum, yet has distinctive traits, including largely aspiny projection neurons that directly innervate the thalamus and a cell type that physiologically resembles neurons recorded in the mammalian globus pallidus. We have proposed that area X is a mixture of striatum and globus pallidus and has the same functional organization as circuits in the mammalian basal ganglia. Using electrophysiological and anatomical approaches, we found that area X contains a functional analog of the "direct" striatopallidothalamic pathway of mammals: axons of the striatal spiny neurons make close contacts on the somata and dendrites of pallidal cells. A subset of pallidal neurons project directly to the thalamus. Surprisingly, we found evidence that many pallidal cells may not project to the thalamus, but rather participate in a functional analog of the mammalian "indirect" pathway, which may oppose the effects of the direct pathway. Our results deepen our understanding of how information flows through area X and provide more support for the notion that song learning in oscines employs physiological mechanisms similar to basal ganglia-dependent forms of motor learning in mammals.
Farries
Michael A
MA
Department of Biology, University of Washington, Seattle, Washington 98195-6515, USA.
Ding
Long
L
Perkel
David J
DJ
D000818:Animals; D001479:Basal Ganglia / Q000502:physiology*; D004525:Efferent Pathways / Q000502:physiology*; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004594:Electrophysiology; D046369:Finches / Q000502:physiology*; D005456:Fluorescent Dyes; D018698:Glutamic Acid / Q000502:physiology; D008297:Male; D011963:Receptors, GABA-A / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology; D009626:Terminology as Topic; D014828:Vocalization, Animal / Q000502:physiology*
D005456:Fluorescent Dyes; D011963:Receptors, GABA-A; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid