Attending to a single stimulus in a complex multisensory environment requires the ability to select relevant information while ignoring distracting input. The underlying mechanism and involved neuronal levels of this attentional gain control are still a matter of debate. Here, we investigated the influence of intermodal attention on different levels of auditory processing in humans. It is known that the activity of the cochlear amplifier can be modulated by efferent neurons of the medial olivocochlear complex. We used distortion product otoacoustic emission (DPOAE) measurements to monitor cochlear activity during an intermodal cueing paradigm. Simultaneously, central auditory processing was assessed by electroencephalography (EEG) with a steady-state paradigm targeting early cortical responses and analysis of alpha oscillations reflecting higher cognitive control of attentional modulation. We found effects of selective attention at all measured levels of the auditory processing: DPOAE levels differed significantly between periods of visual and auditory attention, showing a reduction during visual attention, but no change during auditory attention. Primary auditory cortex activity, as measured by the auditory steady-state response (ASSR), differed between conditions, with higher ASSRs during auditory than visual attention. Furthermore, the analysis of cortical oscillatory activity revealed increased alpha power over occipitoparietal and frontal regions during auditory compared with visual attention, putatively reflecting suppression of visual processing. In conclusion, this study showed both enhanced processing of attended acoustic stimuli in early sensory cortex and reduced processing of distracting input, both at higher cortical levels and at the most peripheral level of the hearing system, the cochlea.

Moderate physical activity improves various cognitive functions, particularly when it is applied simultaneously to the cognitive task. In two psychoneuroendocrinological within-subject experiments, we investigated whether very low-intensity motor activity, i.e. walking, during foreign-language vocabulary encoding improves subsequent recall compared to encoding during physical rest. Furthermore, we examined the kinetics of brain-derived neurotrophic factor (BDNF) in serum and salivary cortisol. Previous research has associated both substances with memory performance.In both experiments, subjects performed better when they were motorically active during encoding compared to being sedentary. BDNF in serum was unrelated to memory performance. In contrast we found a positive correlation between salivary cortisol concentration and the number of correctly recalled items. In summary, even very light physical activity during encoding is beneficial for subsequent recall.

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Abel C, Wittekindt A, Kössl M. Contralateral acoustic stimulation modulates low-frequency biasing of DPOAE: efferent influence on cochlear amplifier operating state? J Neurophysiol 101: 2362-2371. First published March 11, 2009 doi:10.1152/jn.00026.2009. The mammalian efferent medial olivocochlear system modulates active amplification of low-level sounds in the cochlea. Changes of the cochlear amplifier can be monitored by distortion product otoacoustic emissions (DPOAEs). The quadratic distortion product f2-f1 is known to be sensitive to changes in the operating point of the amplifier transfer function. We investigated the effect of contralateral acoustic stimulation (CAS), known to elicit efferent activity, on DPOAEs in the gerbil. During CAS, a significant increase of the f2-f1 level occurred already at low contralateral noise levels (20 dB SPL), whereas 2f1-f2 was much less affected. The effect strength depended on the CAS level and as shown in experiments with pure tones on the frequency of the contralateral stimulus. In a second approach, we biased the position of the cochlear partition and thus the cochlear amplifier operating point periodically by a ipsilateral low-frequency tone, which resulted in a phase-related amplitude modulation of f2-f1. This modulation pattern was changed considerably during contralateral noise stimulation, in dependence on the noise level. The experimental results were in good agreement with a simple model of distortion product generation and suggest that the olivocochlear efferents might change the operating state of cochlear amplification. I N T R O D U C T I O NOuter hair cells (OHCs) are one of the key elements of nonlinear cochlear amplification, which is responsible for high inner ear sensitivity and exquisite frequency resolution (for review see Ashmore 2008;Dallos et al. 2006;Robles and Ruggero 2001). They are densely innervated by efferent fibers that originate in the brain stem and can modulate the electromotile response characteristics of OHC and cochlear mechanics (reviews: Guinan 1996; Russell and Lukashkin 2008). Details of the physiological mechanisms of the medial olivocochlear (MOC) efferent system, its influence on the cochlear mechanics, and its biological function are still under discussion. Activation of the olivocochlear bundle has a substantial, predominantly suppressive effect on basilar membrane motion (e.g., Cooper and Guinan 2003;Murugasu and Russell 1996;Russell and Murugasu 1997) and auditory nerve activity (e.g., Guinan and Gifford 1988a;Guinan et al. 2005;Wiederhold and Kiang 1970) in response to low-level tones. The influence of efferent activity on the cochlear amplification can be investigated by recording otoacoustic emissions (for review see Guinan 2006) that are generated as a by-product of amplification of low-level sound by outer hair cells (Kemp 2002;Probst et al. 1991).In the present study, distortion product otoacoustic emissions (DPOAEs), evoked by simultaneously stimulating the ear with two pure-tone stimuli (primary tones) of differen...