Functional connectivity of the basal ganglia and amygdala

This part three of my neuroanatomy essay, with references. Look here for part one and part two.

(image via Nature)

Functional Connectivity of the Basal Ganglia and Amygdala

Functional Connectivity of the Basal Ganglia

The connectivity and function of the basal ganglia as a structure involved in motor control is well-defined, and has been implicated in such neurodegenerative diseases such as Huntington’s and Parkinson’s. There exist two such pathways within the basal ganglia.

The direct motor pathway begins at the striatum, which receives inputs from both the cortex and the substantia nigra pars compacta. Activation here leads to inhibition, via GABA projections, of the internal globus pallidus. Normally this area tonically inhibits the thalamus, meaning that activation of the striatum leads indirectly to activation (or lack of inhibition) of the thalamus, which can then excite cortical areas. Consequently, the direct pathway acts as positive feedback for motor control. The indirect motor pathway also starts with the striatum and its cortical/nigral inputs. However, the indirect pathway first sends inhibitory projections to the external globus pallidus. Normally the external globus pallidus tonically inhibits the subthalamic nucleus, which transiently activates the internal globus pallidus. In other words, activation of the striatum leads to activation of the internal globus pallidus via the indirect pathway; this in turn leads to further tonic inhibition of the thalamus and its projections to cortical areas. Hence, the indirect motor pathway acts as a negative feedback on motor control.

Functional Connectivity of the Amygdala

The amygdala has been implicated in mood regulation and mood disorders, as one may predict from its pattern of connectivity with the rest of the central nervous system. Foremost, the amygdala receives and reciprocates a large number of sensory inputs (Price, 2003). These include olfactory input (olfactory bulb and olfactory cortex to the cortical nucleus and basomedial nucleus), taste and visceral inputs (brainstem and cortex to central and lateral nucleus), as well as visual and auditory input (sensory cortex to lateral nucleus). In addition to the diverse input and reciprocal output, the amygdala also projects to other central nervous system areas. These include the periaqueductal gray (from central and basomedial nucleus), braintstem (central nucleus), and hypothalamus (medial, central, basolateral and basomedial nuclei). Furthermore, the amygdala forms an interconnective loop with the medial forebrain, thalamus, and basal ganglia. This high level of interconnectivity would suggest a structure that does not act in isolation, but that is intimately involved with several aspects of cognitive and affective behavior.

References

Alheid GF, Heimer L (1988). New Perspectives in basal forebrain organization of special relevance for neuropsychiatric disorders: the striatopallidal, amygdaloid, and corticopetal components of substantia innominata. Neuroscience, 27: 1-39.

de Olmos JS (2004). “Amygdala” in The Human Nervous System, Second Edition, Eds. Paxinos G, Mai JK: Elsevier Academic Press, London.

Haber SN, Gdowski MJ (2004). “The Basal Ganglia” in The Human Nervous System, Second Edition, Eds. Paxinos G, Mai JK: Elsevier Academic Press, London.

Koob GF (2003). Neuroadaptive mechanisms of addiction: studies on the extended amygdala. European Neuropsychopharmacology, 13: 442-452.

Kruger L, Saporta S, Swanson LW (1995). Photographic Atlas of the Rat Brain: Cambridge University Press, Cambridge.

Paxinos G, Watson C (1997) The Rat Brain in Stereotaxic Coordinates, Compact Third Edition: Academic Press, London.

Price JL (2003). Comparative aspects of amygdala connectivity. Annals of the New York Academy of Science, 985: 50-58.

Waraczynski W (2006). The central extended amygdala network as a proposed circuit underlying valuation. Neuroscience and Biobehavioral Reviews, 30: 472-496.