| Coma & Chronic Disorders of Consciousness  

Habituation to auditory startle as a new sign of the minimally conscious state, and neurophysiological evidence for cortical effects of transcranial electric stimulation

Habituation of auditory startle reflex should be considered as a sign of the minimally conscious state, as unresponsive patients who demonstrate this behaviour show increased brain activity and better outcomes compared to patients with inextinguishable startle reflexes.

The improvements observed following transcranial direct current electrical stimulation in some brain-injured patients are associated with increased EEG markers and correlate with the intensity of cortical electric field next to the stimulation electrodes.

Dr. Bertrand Herrmann and his colleagues in Paris (France) have proposed a new auditory clinical sign of the minimally conscious state. The researchers observed that the auditory startle reflex in response to noise presented a habituation in patients capable of anticipating stimulus repetition, who could successfully inhibit the blink when the stimulus was repeated. Conversely, an inextinguishable startle response was present in patients whose detailed clinical examination and cerebral explorations (high-density qEEG, evoked potentials, diffusion tensor MRI, FDG-PET) revealed very poor brain and cognitive activity. The presence of this clinical sign also correlated with prognosis at six months. The authors therefore suggest a systematic assessment of this simple new sign of consciousness in the routine clinical examination of patients with DoC (1)


The same French team has recently demonstrated that the clinical improvement following transcranial direct current electrical stimulation (tDCS) observed in some brain-injured patients, was associated with an increase in specific EEG markers (long distance oscillations and theta communication between prefrontal and parietal regions). They further showed that the response to tDCS was correlated with the simulation of the electric current’s intensity in the cortex. These results encourage the development of new personalized patterns for tDCS stimulation and confirm the importance of the prefrontal cortex and the fronto-parietal network in the physiology of consciousness (2).


Key Points:

  • The habituation to auditory startle reflex could be considered as a new sign of the minimally conscious state, which should be systematically tested in this population
  • Patients with conscious awareness are able to inhibit the blink reflex after repeated stimulation, while those presenting inextinguishable startle reflexes show very poor brain activity and a worse prognosis at 6 months.



Bertrand Hermann, Amina Ben Salah, Vincent Perlbarg, Mélanie Valente, Nadya Pyatigorskaya, Marie-Odile Habert, Federico Raimondo, Johan Stender, Damien Galanaud, Aurélie Kas, Louis Puybasset, Pauline Perez, Jacobo D Sitt, Benjamin Rohaut, Lionel Naccache, Habituation of auditory startle reflex is a new sign of minimally conscious state, Brain, Volume 143, Issue 7, July 2020, Pages 2154–2172, https://doi.org/10.1093/brain/awaa159


Hermann, B., Raimondo, F., Hirsch, L. et al. Combined behavioral and electrophysiological evidence for a direct cortical effect of prefrontal tDCS on disorders of consciousness. Sci Rep 10, 4323 (2020). https://doi.org/10.1038/s41598-020-61180-2