Noise and Vibration

Virtually all laboratory animals are confined for their entire lives, so it is especially challenging to provide one of the five freedoms¹—freedom to express normal behaviour. Compounding the matter, it is increasingly difficult to settle on the parameters of normal behaviour. Recent research strongly suggests that emotions such as empathy may well predate Homo sapiens and extend at least to all species of the mammalian world². And, there is a growing body of research on subtle factors of habitat that may transform normal behaviour. For example, cage bedding may depress sleeping time and induce drug-metabolising enzyme activity, or not, depending on the material, the degree of processing and the size of pieces.

So, the normal behaviour checklist is getting longer and the items on the list are ever more nuanced, which we believe is good for at least two reasons. We are building a richer, more complete picture of animal behaviour and a deeper understanding of environmental factors that may affect it.

Sounds, Audition and Vocalisation
Overall, here’s what important about sound in the lab rat environment: a rat’s greatest sensitivity is to frequencies which are inaudible to us, and rats produce many sounds we can’t hear. So human activity may unintentionally influence behaviour; and, we may incorrectly interpret or explain behaviour we observe.

Here’s why that could happen. Though it depends on the intensity of sound and health of the ears, in general humans perceive frequencies from 20–20,000 Hz4 with 400–4,800 Hz being the range of human speech; rats produce and hear frequencies which we can’t hear, above 20 kHz, and perceive sound up to 80 kHz.

Specifically, rats detect low frequencies (under 500 Hz) less easily, but detect high frequencies (over 8,000 Hz) much more easily than we do. Inner ear cell types do vary across animal strains, and variables such as age, prior exposure, physiological state of the animal and source of sound influence the degrees of response on audiogram (Figure 1).

Figure 1: Hearing ranges of everyday laboratory animals.⁴