MSc Neuroscience

September 2018

Polaris Group

Is Positive Electrical Stimulation Associated with Ultrasonic Vocalization in Rats?

Introduction Research has shown that rats make ultrasonic vocalizations (USV) in anticipation of electrical stimulation of the brain (Burgdorf, et al., 2000). Positive affect can be elicited with electrical stimulation of the medial forebrain bundle in the rat as indicated by the production of 50-kHz Ultrasonic vocalizations. Burgdorf, et al., (2011) reports that frequency modulated (FM) ultrasonic vocalizations are associated with positive affect and bursts from dopaminergic neurons. Fourteen categories of 50-kHz USV’s have been identified but of the fourteen categories only three categories, the frequency modulated ultrasonic vocalizations (trill, flat, and step), are predominant and associated with positive affect. The specific categories of frequency modulated vocalizations have not been identified in anticipation of electrical stimulation of the medial forebrain bundle. I suspect that only one or two frequency modulated calls are associated with reinforcement.

Theory The Biological theory of reinforcement states that behaviors have evolved as a mechanism for species-typical responses to appropriate stimuli.
Evidence suggests that response sequences are organized in the brain stem of the mammal.

Hypothesis Electrical Stimulation of the brain is reinforcing and is associated with behavior that signals reinforcement such as by Ultrasonic Vocalizations.

Method Subjects are twelve Long–Evans hooded adult male rats from the University of Lethbridge animal colony used in compliance with the guidelines of the University of Lethbridge Animal Care Committee and the Canadian Council for Animal Care. All subjects will have bipolar twisted pair stainless steel wire electrodes with tip separated by 0.5 mm implanted bilaterally. The subjects are divided into 2 groups; six receive stimulation and six are control animals which have implants but receive no stimulation.

Rats are individually placed in an operant chamber with a nose poke optical switch. The operant chamber is located inside a sound proof exterior chamber which has a microphone centered at the top. A nose poke will turn on electrical stimulation to the medial forebrain bundle fiber track and ultrasonic vocalization will be recorded.

Simulation is on for 20 minutes followed by 10 minutes of extinction where no stimulation is available. Histology will be performed to identify the location of simulation electrodes.

Results USV frequency patterns identify three categories of USV (trill, flat, and step) associated with ESB. ESB of the MFB results in more nose poke behavior and increasing 50 k-Hz ultrasonic vocalizations within the FM category.

Future Directions

Stimulate other nuclei and fiber pathways in the hindbrain and midbrain to compare areas of the brain with reinforcing ESB and FM USV.


Burgdorf J, et al., 2000. Behavioral Neuroscience; 114: 320-327

Burgdorf J, 2011. Neuroscience and Biobehavioral Reviews; 35: 1831–1836