Age, Speech and Brain

Communication is an essential part of our everyday life. Conversations allow us to share our opinions and needs, share experiences and generally maintain social contacts. At an advanced age, however, the situations in which one needs to ask one's conversational partner to repeat the sentence become more frequent. This is due to age-related hearing loss, which affects many older people. In order to counteract the difficulties in understanding spoken language, hearing aids are used. Often, however, these devices are not sufficient to compensate for the impairment in everyday communication.

The reduction in speech comprehension in old age can have multiple causes: the auditory system loses flexibility and functionality; cognitive abilities such as memory and attention are reduced by aging processes in the brain.

Comprehension problems seem to be particularly severe when one needs to perceive spoken language in a noisy environment. Studies have shown that difficulties in understanding spoken language occur even when no peripheral hearing loss is apparent. This means that aging and age-related decline impair the function of the auditory cortex in the absence of deficits in the auditory organ itself. Peripheral hearing loss thus seems to play only a secondary role.

Nevertheless, these two aspects should be considered both independently of each other and in their interaction. Long-term studies indicate that the nerve cells in the auditory cortex degenerate due to deteriorated functionality of the auditory organ. It is assumed that the thinning of connections between nerve cells in the brain's right hemisphere in particular is associated with age-related hearing loss. These brain areas are responsible for processing paralinguistic aspects of spoken language, namely intonation, rhythm and intensity. Consequently, the organization of speech processing in the brain is distributed over a large neural network, which seems to be subject to age-related changes. There are indications that the patterning of this network during speech processing differs between older and younger people.

Thus, in the case of hearing loss, it is necessary to take both deficits in the hearing apparatus and, the anatomy of the aging brain into account because both a functioning hearing organ and central brain functions are needed to process and understand the perceived speech signals.

Age-related hearing loss is a normal aging process. However, many questions concerning the relationship between speech comprehension and cognitive ability in old age, as well as the impact of hearing loss on this interplay, remain unanswered. Additionally, there is the phenomenon of tinnitus, which often occurs in old age and which can also have an influence on speech comprehension (see section "How does tinnitus affect speech understanding?" for more information). Our current research is contributing to the understanding of how to maintain speech comprehension and hearing in old age.

The main objective of our studies is to describe the interplay between the different factors affected by age-related decline (e.g. brain, hearing, cognition, tinnitus) and their influence on the understanding of speech in old age. The aim is to show how hearing loss, tinnitus and reduced cognitive performance complicate speech processing, and to explore to what extent hearing aids, additional information through lip-reading and well-preserved cognition can have compensatory effects.

A subjective tinnitus describes the perception of a permanent sound that lacks an, external acoustic stimulus. These hearing sensations are widespread and heterogeneous in that they vary from person to person. Variations can occur in the sensation itself as well as in its accompanying symptoms. Some of those affected  describe their tinnitus as a humming, buzzing, ringing or rustling sound, others as a kind of rushing, and still others report perceiving a pure-tone in one or in both ears. In addition to these characteristics, the volume, pitch and subjective intensity of these sensations may also vary.

An equally broad heterogeneity can be found in the causes and in the development process of tinnitus. It is well known that tinnitus is often the result of noise trauma or age-related hearing loss. Therefore, it is increasingly common that older people are affected by tinnitus.

People with chronic tinnitus usually learn to live with their background noise. Fortunately, relatively few of those affected experience serious consequences to their quality of life, usually because they have no subjective control over the sensory perception and thus feel that they are at the mercy of the tinnitus. The term "tinnitus stress" is used when the hearing sensation is perceived as disturbing, intrusive and annoying by the person affected. This perception, however, is not limited to the role played by emotional aspects. If the burden of tinnitus reaches a high level, the affected person can also be limited in their cognitive abilities - such as concentration or memory - which can have considerable consequences on their everyday and professional life. The severity of such stress is purely subjective and cannot be deduced from the assessed properties of tinnitus.

A common side effect of tinnitus is difficulty understanding spoken language in a noisy environment. This becomes apparent in everyday situations such as waiting at the station, taking coffee breaks in the office or at a restaurant, attending sales talks, or playing with grandchildren on the playground. Frequently during the course of the day, we find ourselves in noisy environments and are constantly confronted with sounds. Understanding spoken language becomes more challenging as age and hearing loss levels increase. Older tinnitus patients frequently report that they find it difficult to follow a conversation or that they quickly become tired. This can even be the case for people who suffer from tinnitus but do not have a diagnosed hearing loss.

According to a study by our research group, the extent of subjective tinnitus stress is associated with the ability to understand speech in noisy environments. This means that a person who considers their tinnitus stress to be low performs better in understanding spoken language compared to a person who feels strongly stressed due to their tinnitus. The exact underlying causes of this association remain mostly unclear. Further investigations into whether these difficulties in understanding are due to disturbances in auditory processing, or to a deficit in cognitive functioning are needed. For example, it is possible that a tinnitus could have an effect on the inhibitory control of the cerebrum, especially in the case of high subjective stress. Redirecting and controlling attention thus becomes problematic, because the affected person focuses excessively on the ringing in their ears instead of focusing on bringing the relevant information to the fore. Due to this imbalance and an excessive sensitivity to the source of noise (which is suspected to be a side effect of high tinnitus stress)the affected person becomes caught in a vicious circle, which makes the understanding of spoken language considerably more difficult.

Many questions in connection with tinnitus and its accompanying symptoms remain unanswered. Subjective sensory perceptions are not easy to categorize. Therefore, research in this field faces a great challenge to contribute to a better understanding of the heterogeneity of tinnitus symptoms.

In a recent study using electroencephalography (EEG), hearing and behavioral tests, we aim to find out to what extent different factors such as tinnitus, hearing loss and cognition (e.g. attentiveness) are involved and how they interact in the understanding of speech.