Long term effect of using noise generators

Question

Some people use noise generators as http://playnoise.com/ to reduce distraction by background noise. Is there any research on the long term effects of this? Does this affect the neuronal connections in a known way?

[I don't know, but I suspect that longer exposure to senseless information (noise) should have an effect on some part of the brain. I am also suspecting that if "low-level senseless information" (i.e. static noise) has an effect, "high-level senseless information" (i.e. random combinations of patterns) could have a similar effect on a deeper cognitive level, but that is wild guessing.]

Answer 1

Short answer

Yes, continuous exposure to white noise affects neural responses in the auditory system. First, it can alter the tonotopic map in the auditory cortex. Second, it can lead to reduced responsiveness of the auditory thalamus.

Background

Note: this answer is based on animal experiments using extreme conditions, namely a continuous noise exposure for at least a month.

The most striking effect of continuous low-level white noise exposure (30 days) is a dramatic reorganization of the tonotopic map in the auditory cortex (Zheng, 2012). Basically, the normally regular distribution of low-to-high frequency representation in auditory cortex was grossly disorganized in noise-treated rats. The noise-treated rats performed better on a pitch-discrimination task in noise than non-treated rats. They performed worse in a quiet environment, though. Hence, their auditory system had adapted to the noise and was optimized for noisy environments.

In another study it was shown that adult rats exposed to noise (50 days) showed increased long-term-depression (LTD) in A1 neurons of the medial-geniculate nucleus (MGN) (Speechley et al., 2007). The MGN is the thalamic processing centre of the auditory pathway (Rees, 2009). Speechley et al. mention the following, and I quote:

The facilitation of depression observed here [..] suggests that in the developed A1 continuous white noise produces general over-excitation of thalamocortical networks, resulting in greater LTD induced by low-frequency inputs to the network.

LTD can be interpreted as a long-term decrease in responsiveness of the auditory system to stimulation. Basically it reacts to the white noise by decreasing its activity. They explain these effects by the fact that white noise can act as a mild stressor, with accompanying changes in neuroendocrine activation and immune function. Stress and related hormonal changes may increase corticosteroid levels that facilitating LTD.

Interestingly, in newborn rats, the same treatment resulted in enhanced long-term potentiation (LTP) of the MGN. The authors raise the following explanation, and I quote:

White noise reared animals showed greater levels of LTP relative to rats raised in unaltered auditory environments. Also, stimulation parameters (single 1-Hz pulses) that induced depression in control animals resulted in robust potentiation in white noise-reared rats, indicating that lack of patterned auditory stimulation during early post-natal life results in a preferential readiness of the auditory thalamocortical system for synaptic potentiation over depression.

References
Rees, Encyclopedia of Neurocience 2009:2275-9
Speechley et al. Eur J Neurosci 2007;26:2576–84
Zheng, Front Syst Neurosci 2012;6:1-14

Answer 2

There is some cool evidence (e.g., Canlon et al. 1988) that low level noise exposure can actually protect you against high level noise exposure. That said, I am not sure that one should constantly expose themselves to low level sounds in the hope that it will protect them from high level sounds. Melamed et al. (1996) found that long term exposure to moderate sound levels (85 dB) can increase cortisol levels, fatigue and irritability.