Event-specific enhancement of memory via brief electrical stimulation to the basolateral complex of the amygdala in rats

Abstract

The basolateral complex of the amygdala (BLA) modulates memory for emotional events, and direct activation of the BLA following a learning session can enhance subsequent memory. Yet optimal enhancement of episodic memory during emotional events would likely require that BLA activation occur close in time to the event and to be brief enough to target specific memories if some events are to be remembered better than others. In the present study, rats were given a novel object recognition memory task in which initial encounters with some of the objects were immediately followed by brief electrical stimulation of the BLA, and these objects were remembered better one day later as compared to objects for which the initial encounter was not followed by stimulation. The results indicated that BLA stimulation can enhance memory for individual events, a necessary ability for the BLA to modulate episodic memory effectively.

Conflict of interest statement

Conflict of Interest: none

Figures

Figure 1

Schematic of the novel object recognition memory task. Rats encountered three groups of objects in each phase: Stimulation objects (denoted by an “S”), for which brief electrical stimulation was delivered to the BLA immediately after a rat disengaged from exploration during the Study Phase only and which were repeated during one test, “No Stimulation” objects (denoted by an “O”), which were also repeated during one test, and “New” objects (denoted by an “N”), which were not repeated. Objects presented on the Immediate Test were not included on the 1-Day Test. Objects within a trial were presented on the same lap during the Immediate Test and during the 1-Day Test but were presented on separate laps during the Study Phase in order to better isolate the influence of amygdala stimulation to a particular object. Rats completed a lap on an empty track between each trial on all three phases (see Method for details).

Figure 2

Performance on recognition memory tests shown as a discrimination index (n=9). A. Rats remembered repeated objects well during the Immediate Test, but remembered repeated objects during the 1-Day Test only if exploration of those objects during the Study Phase had been followed by brief electrical stimulation of the BLA. B. Sham Stimulation did not significantly alter memory on either the Immediate Test or the 1-Day Test as compared to No Stimulation. The dashed line indicates chance performance. Error bars show SEM. * = p < 0.05, ** = p < 0.01.