Optogenetic dissection of amygdala functioning.

Ryan T Lalumiere

doi:10.3389/fnbeh.2014.00107

Abstract

Studies of amygdala functioning have occupied a significant place in the history of understanding how the brain controls behavior and cognition. Early work on the amygdala placed this small structure as a key component in the regulation of emotion and affective behavior. Over time, our understanding of its role in brain processes has expanded, as we have uncovered amygdala influences on memory, reward behavior, and overall functioning in many other brain regions. Studies have indicated that the amygdala has widespread connections with a variety of brain structures, from the prefrontal cortex to regions of the brainstem, that explain its powerful influence on other parts of the brain and behaviors mediated by those regions. Thus, many optogenetic studies have focused on harnessing the powers of this technique to elucidate the functioning of the amygdala in relation to motivation, fear, and memory as well as to determine how the amygdala regulates activity in other structures. For example, studies using optogenetics have examined how specific circuits within amygdala nuclei regulate anxiety. Other work has provided insight into how the basolateral and central amygdala nuclei regulate memory processing underlying aversive learning. Many experiments have taken advantage of optogenetics’ ability to target either genetically distinct subpopulations of neurons or the specific projections from the amygdala to other brain regions. Findings from such studies have provided evidence that particular patterns of activity in basolateral amygdala (BLA) glutamatergic neurons are related to memory consolidation processes, while other work has indicated the critical nature of amygdala inputs to the prefrontal cortex and nucleus accumbens (NA) in regulating behavior dependent on those downstream structures. This review will examine the recent discoveries on amygdala functioning made through experiments using optogenetics, placing these findings in the context of the major questions in the field.

Highlights

Optogenetic dissection of amygdala functioningReviewed by: Christa McIntyre, University of Texas, USA Joshua Johansen, RIKEN Brain Science Institute, Japan
Studies of amygdala functioning have occupied a significant place in the history of understanding how the brain controls behavior and cognition
Previous work had suggested that the medial central amygdala (CEA) and its inputs from the basolateral amygdala (BLA) drive anxiety and/or fear-related behaviors, whereas BLA inputs to the lateral CEA provide feedforward inhibition of the medial CEA (Paré et al, 2004; Ciocchi et al, 2010)

Summary

Optogenetic dissection of amygdala functioning

Reviewed by: Christa McIntyre, University of Texas, USA Joshua Johansen, RIKEN Brain Science Institute, Japan. In contrast to many studies that have used 20 Hz stimulation but consistent with our own work (e.g., Huff et al, 2013), Carter et al found that 20 Hz stimulation did not produce as strong a behavioral effect as found with the 30 and 40 Hz stimulation By utilizing both the genetic targeting ability of combining optogenetics with transgenic mice and by targeting the axon terminals, these findings provide a significant step forward in understanding how genetically distinct neuronal populations connect with different regions in the brain and, in turn, regulate appetite-related behavior. These findings were demonstrated in a specific subclass of interneurons, an important issue as other work has suggested that different stimuli influence different subtypes of interneurons in the BLA (Bienvenu et al, 2012)

CONCLUSIONS

Area of investigation