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The neurophysiology of auditory perception

Project coordinator: Carles Escera.

Project members:  Judith Domínguez-Borràs, Iria SanMiguel, Manuel Garcia-Garcia, Sabine Grimm, Lavinia Slabu, Jordi Costa-Faidella, Heike Althen, César Ávila.

 

       

GOALS OF THE PROJECT  

Prevailing models of the human auditory function, mostly based on the mismatch negativity (MMN) evoked potential, establish that the auditory system automatically scans the acoustic environment for regularities, builds cortical memory traces of them and detects deviant stimuli by comparison of the current input against the model. This makes it possible to: 1) build auditory perceptual objects, and 2) draw attention to unexpected potentially relevant stimuli. This project investigates the precise implementation of this model in the auditory nervous system and its interactions with higher forms of cognitive control.

SUBPROJECT 1: Levels of novelty detection in audition. While a large body of evidence suggests that the MMN is cortical in origin, recent animal studies have described individual neurons showing the ability to detect novel stimuli, through stimulus-specific adaptation (SSA), in subcortical auditory nuclei such as the medial geniculate body and even the inferior colliculus. This raises the question of whether this kind of subcortical novelty detection is also present in humans, supporting a hierarchical organization of auditory novelty detection. Grimm et al. (2010) and Slabu et al. (2010) managed to find a correlate of human novelty detection in the latency range of the middle latency auditory evoked potential, circa 30-40 ms from deviance onset (Figure 1), matching the latency and origin of novelty responses in animals. Moreover, preliminary results from our group have revealed novelty-related specific activation in the human inferior colliculus by means of functional magnetic resonance imaging (fMRI).

           

 

 

Figure 1.  The middle-latency response to same physical deviant, standard and control (ie, controlling for refractoriness) stimuli showing true novelty detection in the latency range of the Nb waveform, circa 40 ms from deviance onset (Grimm et al., 2010).

SUBPROJECT 2: Top-down modulation of auditory novelty processing. It is well known that the MMN generating system issues a call for attention that disrupts current performance in an automatic manner. However, it is a common experience that involuntary attention to unexpected sounds depends on ongoing activities. Here, we have shown that loading working memory can reduce involuntary attention to auditory distracters (SanMiguel et al.  2010), and conversely, that facing a negative emotional context enhances distraction and the corresponding neural signatures of novelty processing, such as the novelty-P3 (Domínguez-Borràs et al., 2008), the synchronization of the gamma band response (Garcia-Garcia et al., 2010b; Figure 2) or the novelty-related activity in superior temporal gyrus (Domínguez-Borràs et al., 2010; Figure 3). Moreover, these top-down modulatory effects are dependent on the dopamine neurotransmitter system, as revealed by genetic studies (Garcia-Garcia et al., 2010a).

                          

Figure 2.  Enhanced synchronization of the gamma band res-

ponse at 40Hz in the latency range of 50-150 ms to audi-

tory novelty in a negative  emotional context compared  

to a neutral emotional condition  (Garcia - Garcia et al.,

2010b).

                                                                                                             

  

Figure 3.  Enhanced auditory novelty processing in the superior temporal gyrus in a negative emotional context (Domínguez-Borràs et al., 2009).