One strand of research at MARCS involves investigating various aspects of tinnitus (when a person perceives an on-going sound in the absence of an external sound source).
As Susan Rossiter (the lead author of one study) has been quoted "we wanted to learn more about the ways in which chronic tinnitus disrupts cognitive performance". In this study (with Gary Walker and Kate Stevens) 38 people, half of whom had constant moderate to severe tinnitus, and an age-, educational level-, occupation-, and verbal IQ -matched control group, completed auditory verbal working-memory and visual divided-attention tasks. The results showed that the reading span of the tinnitus group was significantly lower than that of the control group. Furthermore, the tinnitus group had slower reaction times and poorer accuracy in the most demanding dual task context. It was concluded that complaints concerning the distracting effects of tinnitus have a basis in performance test outcomes. A follow-up study (Stevens, Walker, Boyer & Gallagher , 2007) investigated other important variables that might have affected cognitive performance such as depression and hearing loss. Here, the results supported a general depletion of resources hypothesis with the reaction times of the tinnitus group slower in the Stroop task, and in the word reading and category naming conditions of a dual task. As Gary Walker has said "our ultimate goal is to use this knowledge to develop management strategies that will help minimize disruption”.
But what is the cause of tinnitus and how might knowledge of this cause help to tailor treatments? A recent review paper, Kaltenbach (2009) identifies three components of tinnitus: the acoustic (the unwanted sound itself); the attentional (the degree to which a person listens to/or focuses on the tinnitus) and the emotional component (the affective reaction to the tinnitus). In terms of mechanism, the basic idea is that tinnitus is caused by plastic changes that affect the normal balance of excitatory and inhibitory inputs to neurons.
Kaltenbach presented a simple figure outlining the contemporary view of changes in the brain that appear to contribute to tinnitus percepts. First thing to note is the cochlear damage (hair cells). This has follow-on effects on the neurons of the hind, mid and forebrain. How a loss of hearing or of normal cochlear function causes the changes in neural pathways thought to underlie tinnitus is not well understood, but changes in frequency mapping, neural synchrony and hyperactivity (loss of inhibition) have all been implicated.
In a recent PNAS paper, Okamoto, Stracke, Stoll and Pantev (2009) have built on the idea of maladaptive auditory cortex reorganization and proposed a treatment approach that targets the tinnitus percept directly. This treatment approach was based on the results of a previous study (Pantev, Wollbrink, Roberts, Engelien, Lütkenhöner, 1999) that showed that listening to spectrally “notched” music can reduce cortical activity corresponding to the notch centre frequency (although this approach seems curiously at odds with that taken by Norena & Eggermont, 2006).
Okamoto and colleagues tested 23 people in a double-blind trial that lasted for one year. Eight participants received the treatment (see below). Another eight received a placebo and seven participants were simply monitored without any treatment. The treatment method used involved first establishing the central frequency of the tinnitus percept (to do this the authors selected people who experienced strongly lateralized tonal tinnitus – like a beep or whistle – with participants ipsi-laterally matching the tinnitus pitch to the frequency of a pure tone at least four times on two different days. The median across pitch match was used as the tinnitus frequency). Each participant then selected a favourite piece of music.
For the treatment group, this piece of music was then altered so that the frequencies one octave on either side of the participant’s tinnitus pitch were removed (see figure). The placebo group received a “placebo music” modification in which a moving filter of one octave width that spared the tinnitus frequency region was used (i.e., the moving filter randomly chose a frequency band outside the one octave wide tinnitus frequency region). Following this, participant’s listened to this "notched" piece of music every day for a year (listening times were documented daily). Here are two example of the music:
Target notched music treatment
Placebo notched music treatment (using a moving notch filter)
The results showed that after a year, the treatment group felt that their ringing sensation was around 30% quieter, while the other two groups showed no improvements. It was also found that the notched music reduced the activity of the affected neurons within auditory cortex of the treatment group. Here’s the abstract:
Maladaptive auditory cortex reorganization may contribute to the generation and maintenance of tinnitus. Because cortical organization can be modified by behavioral training, we attempted to reduce tinnitus loudness by exposing chronic tinnitus patients to self-chosen, enjoyable music, which was modified (“notched”) to contain no energy in the frequency range surrounding the individual tinnitus frequency. After 12 months of regular listening, the target patient group (n =8) showed significantly reduced subjective tinnitus loudness and concomitantly exhibited reduced evoked activity in auditory cortex areas corresponding to the tinnitus frequency compared to patients who had received an analogous placebo notched music treatment (n =8). These findings indicate that tinnitus loudness can be significantly diminished by an enjoyable, low-cost, custom-tailored notched music treatment, potentially via reversing maladaptive auditory cortex reorganization.
Of course this is a rather small study, but it is the logic that underlies the approach that is interesting (not only in that it addresses acoustic processing using the cortical plasticity framework but by using the participant’s most enjoyable music, it covers both the attentional (encourages engaged attention) and affective (enjoyable) components associated with tinnitus percepts).
Kaltenbach, J.A. (2009) Insights on the origins of tinnitus: An overview of recent research. The Hearing Journal, 62 (2).
Norena A.J. & Eggermont J. (2006). Enriched acoustic environment after noise trauma abolishes neural signs of tinnitus. Neuroreport, 17, 559-563.
Okamoto, Stracke, Stoll & Pantev. (2009). Listening to tailor-made notched music reduces tinnitus loudness and tinnitus-related auditory cortex activity. PNAS doi: 10.1073/pnas.0911268107.
Pantev, C. Wollbrink, A., Roberts, L. E., Engelien, A., Lütkenhöner, B. (1999). Short-term plasticity of the human auditory cortex. Brain Research, 842, 192–199.
Rossiter, S., Stevens, C. & Walker G. (2006). Tinnitus and Its Effect on Working Memory and Attention. Journal of Speech, Language, and Hearing Research, 49, 150-160.
Stevens , C. Walker, G. Boyer M. & Gallagher M. (2007). Severe tinnitus and its effect on selective and divided attention. International Journal of Audiology, 46, 208-216.