The Brain as "the scene of the crime"

Although the human brain weighs a mere 1.5 kilograms it is nonetheless the most complex organ as yet produced by evolution: around 100 billion nerve cells with more than a trillion contact points – so-called synapses – are wired together to form a gigantic network. Whether we are concentrating on a difficult task or fast asleep, our gigantic nerve cell network never stops working and is akin to an ultra-fast data highway: nerve cells communicate and exchange information with each other to control and steer our entire organism. Communication between nerve cells is based on electrical signals – which is why brain activity can be examined by measuring brain waves (EEG = electroencephalography).

Certain neurological diseases (e.g. tinnitus or Parkinson's disease) are characterised by pathological nerve cell hyperactivity and synchronisation: the nerve cells in the affected areas of the brain engage in continuous and excessive synchronised activity with all of the cells firing off electrical signals at the same time. This pathologically synchronised "firing" is what causes the typical symptoms – the tremor of Parkinson's and the continuous sound of tinnitus (1,2).

When nerve cells talk to themselves

Pathological nerve cell activity is triggered by a malfunction of normal signal transmissions which results in an imbalance between stimulating and inhibiting signal information in the affected areas of the nerve cell network. The end result is hyperactivity and synchronisation (1,2). To put it simply, one could describe the cause of tinnitus like this: when the ear stops talking to the nerve cells in the auditory cortex they will start to talk to themselves (1).

The brain's natural synaptic plasticity that enables it to adapt flexibly to changed conditions allows the malfunctioning nerve cell activity to consolidate and become chronic: the brain begins to learn synchronous hyperactivity (3,4).

^{1 L. Roberts, J. Eggermont, D. Caspary, S. Shore, J. Melcher, J. Kaltenbach: Ringing Ears: The Neuroscience of Tinnitus; J Neurosci.; 30(45): 14972–14979 (2010)
2 H. Bergman and G. Deuschl: Pathophysiology of Parkinson’s disease: from clinical neurology to basic neuroscience and back; Mov. Disorders 17 S28–40 (2002)
3 E. Kandel, J. Schwartz, T. Jessell: The Principles of Neural Science; Elsevier (2000)
4 R. Llinás, U. Ribary, D. Jeanmonod, E. Kronberg, P. Mitra: Thalamocortical dysrhythmia: A neurological and neuropsychiatric syndrome characterized by magnetoencephalography; Proc Natl Acad Sci U S A.; 96: 15222-15227 (1999)}