University of Helsinki

History

CBRU was preceded by Cognitive Psychophysiology Research Unit, founded by Prof. Risto Näätänen. The research was focused on two cerebral responses, the mismatch negativity (MMN) and processing negativity (PN), both discovered by Näätänen et al. (1978). The MMN is a change-detection mechanism reflecting cortical sound-discrimination accuracy whereas the PN indicates how the brain selects relevant stimuli for further processing. The MMN has become a popular tool world-wide for cognitive neuroscience, since it can be recorded even from inattentive subjects and applied to a variety groups, including patients, infants, and even foetuses. Already in 2004 it was estimated that there were about 1000 publications in international refereed journals using this brain response.

MMN is elicited by any discriminable change in any repetitive aspect of auditory input irrespective of the subject or patient’s attention or behavioural task, which implicates the occurrence of an automatic comparison between the current input and the representation, or the memory trace, of the preceding auditory events. This change-detection process occurs unconsciously in the auditory cortices (generating the auditory-cortex subcomponent of the MMN) but activates, with a very short time delay, frontal-cortex mechanisms (generating the frontal subcomponent of the MMN) controlling the direction of attention, which leads to attention switch to, and conscious perception of, sound change (Näätänen, Beh. Brain Sciences, 1990). Thus, the MMN is also involved in initiating a cerebral warning mechanism which is of great biological significance.

While the basic mechanism of the MMN is simple, with appropriate experimental manipulations it is a versatile tool for investigating various aspects of auditory perception and attention. Here are some examples on the applicability of the MMN for neuroscience studies:

• The effects of auditory experience can be investigated with the MMN. For instance, the sensitivity of the auditory system is enhanced for familiar sounds, such as to native-language speech sounds (Näätänen et al., Nature, 1997; Winkler et al., Psychophysiology, 1999).
• The neural determinants of musical expertise and musicality can be determined with
  MMN recordings (Tervaniemi et al., Neurosci Lett. 1997; Learn Mem. 2001; NeuroReport
  2006; van Zuijen et al., Brain Res. 2004; Brattico et al., Brain Res., 2006).
• The development of the native-language speech sound representations can be followed-up since the infancy (Cheour-Luhtanen et al., Nature Neurosci., 1998). MMNs for sound changes can be recorded as early as in the foetal stage (Huotilainen et al., NeuroReport, 2005).
• Our auditory system is constantly modelling and making predictions on the auditory scene. Violations of the auditory regularities elicit an MMN even when the individual cannot consciously detect such violations (Näätänen et al., TINS, 2001; van Zuijen et al., J. Cogn. Neurosci., 2006).
• The awakening from coma can be predicted with the MMN (Kane et al., The Lancet, 1993; Fischer et al., Crit Care Med, 2006).
• The MMN reflects plastic changes in the auditory cortex of the blind but does not reflect cross-modal reorganization. This type of reorganization is evident in the processes following the MMN, such as the N2b (Kujala et al., TINS, 2000).
• The MMN reflects plastic neural changes caused by intervention of audiovisual processes in dyslexic children (Kujala et al., Proc. Natl. Acad. Sci., 2001).
Traditionally, the MMN has been recorded with an oddball paradigm, which typically includes a repetitive standard stimulus (e.g., a 1000 Hz tone, p. 0.9) occasionally replaced by a deviant stimulus (e.g., 1100 Hz, p. 0.1). This approach is very time consuming, having always the trade-off of MMN signal quality and the amount of information obtained (the number of different deviant types for which the MMN is recorded). Especially for investigating patient groups and young children this approach is not optimal since the recording times should be kept minimal while the EEG trial loss may be high due to, e.g., movements. To overcome these problems, Näätänen et al., (Clin. Neurophysiol., 2004) developed a new multi-feature MMN paradigm, originally called “Optimum-1”, with which MMN for 5 different types of deviant sounds can be recorded in the same time as for one deviant type in the oddball paradigm described above. The deviants included in such multi-feature sequence are alternating with the standard stimulus and each deviant stimulus should differ from the rest of the stimuli in one feature only. The rationale of this paradigm is that besides serving as a deviant, each deviant stimulus type also strengthens the memory trace for the features it shares with the rest of the stimuli, thereby acting as a “standard”. For example, if only the frequency of a sound changes, this sound still strengthens the memory traces for sound duration, intensity, and location.