What causes auditory sensitivity?
Auditory sensitivity, or auditory hypersensitivity, to sounds can occur for a number of reasons. Sometimes the hearing sensitivity occurs because of a medical condition. Or, there may be a structural problem within the ear itself. It can also occur as a side effect of some medications. If this is the case, then the child or adult will need to seek further support from relevant medical professionals. In this case, it would not be correct to consider the sensitivity as a sensory processing issue.
When there is no medical reason to explain the auditory sensitivity, researchers think that the brain is not processing sounds adequately. Researchers suggest that the part of the brain that receives and filters noise and sound, the amygdala, is working differently. The amygdala decides on how important noises are. It decides and which sounds we should attend to and which ones to ignore.
When someone experiences sensitivity to sounds, it is thought the amygdala pays more attention to sounds than it needs to. Occupational therapists usually refer to this sensory issue as a ‘sensory modulation difficulty’. Sensory modulation is one of the components of Sensory Processing Disorder (SPD). You can read more about SPD on our page, ‘What is Sensory Processing Disorder?’
Occupational therapists may label auditory sensitivity as an ‘over-responsivity to noise’. This is because children and adults with sensitivity to sounds usually have a bigger response or reaction to noises than might be expected by someone who does not experience auditory hypersensitivity. The child or adult might be more easily surprised or startled by sounds than others. Or, they may hear sounds that others in the same space don’t hear. They may find it more difficult to ignore sounds. Or, could become quickly overwhelmed by multiple sounds. This is sometimes called auditory overload.
Auditory overload – the amygdala and its ‘fight flight freeze’ response
The amygdala is a pea sized group of neurons that sit roughly in the centre of the brain. It connects to most of the other parts of the brain. Sensory messages from the body are sent from the amygdala to the relevant parts of the brain. It’s bit like a traffic controller, sending and directing the sensory messages to the part of the brain that needs to process them.
The amygdala is also responsible for keeping the body safe. Sometimes it will trigger an automatic safety response called a ‘fight, flight or freeze’ response. This response is a protective mechanism designed to keep us safe.
The amygdala is the part of the brain that makes us jump if we hear an unexpected sound. It is the part of the brain that tunes in if we hear a noise that we can’t quite locate or identify. It’s the part that makes us instantly more alert if we hear our head teacher’s or manager’s voice. It is also the part of the brain that processes sounds differently in children and adults who are overwhelmed by sounds, noise or audio sensory inputs.
Auditory overload often occurs when there are too many sounds happening at the same time. Or, if the noise is at a certain frequency. In addition, the brain can also become overwhelmed by noise which has occurred over a period of time.
What is going on when there is auditory hypersensitivity?
It is thought that the amygdala (the sensory traffic controller) of children and adults with auditory sensitivity pays much more attention to sounds than expected. Instead of ignoring sounds that aren’t important, it keeps attending to them. This means children and adults with sound sensitivity are more easily distracted to noises in the environment. It can also decrease their ability to focus on the relevant noise (e.g. their teacher talking).
Children or adults with hypersensitivity to noise are also typically more easily alerted by sounds than others. Their sensory traffic controller is more alert and listening out for sounds. When an unexpected sound occurs, instead of directing the sensory messages through to the thinking parts of the brain to understand what it was, the amygdala more readily initiates a fight or flight reaction. This can also occur when someone is anxious. So, a person’s level of anxiety will also affect their level of sensitivity to noise. You might have experienced this if you have ever been walking in the dark in an unfamiliar space. Here, your senses would typically be more heightened, and you may overreact to a sound which you otherwise would not. For example, a bird singing might give you a fright.
Their amygdala can also more quickly overwhelmed by sounds. This could be because it finds it more difficult to process all of the noises at once. It could also be because paying attention to all of the audio information in the space, it is processing a lot more information at the same time.