Elsevier

Clinical Neurophysiology

Volume 119, Issue 8, August 2008, Pages 1795-1802
Clinical Neurophysiology

The effect of aging on auditory components of event-related brain potentials

https://doi.org/10.1016/j.clinph.2008.04.007Get rights and content

Abstract

Objective

To describe auditory perceptual, pre-attentive, attention-related and cognitive processes along lifespan in normal people by a simple auditory oddball paradigm easily usable in clinical practice.

Methods

ERPs were recorded in 72 normal subjects. Four blocks of tones were delivered (20% rare 2000 Hz and 80% frequent 1000 Hz). In the former two blocks, subjects performed a concomitant distracting visual search task (distracted condition); in the latter two blocks, they had to attend the occurrence of the rare tones (active condition). Latency and amplitude of ERPs were analyzed according to age, gender, educational level and repetition.

Results

N100 amplitude was greater in active than in distracted condition. MMN amplitude decreased with age. N2b and P300 latencies increased with age, while their amplitudes decreased. Females produced greater P300 than males. In the elderly, P300 latency was found to be longer in the second block than in the first one.

Conclusions

N100 and MMN were found to be less affected by age than N2b and P300. When repeated, P300 showed increased latency in elderly subjects.

Significance

The protocol detected the higher influence of aging on late cognitive processes than on the perceptual and pre-attentive ones. Age-adjusted normative data were produced.

Introduction

The study of age-related cognitive changes is becoming an important scientific and social issue, due to the prolonged life expectancy of the human population and the consequent need of an early discrimination between normal and pathological brain aging for precocious treatment of cognitive alterations and dementia (Salthouse, 1991; Golob et al., 2002; Katada et al., 2004).

Event-related brain potentials (ERPs) provide important clues to understand normal and abnormal brain aging, because they reflect the time-course of perceptual, attention-related, and cognitive process before their behavioural manifestation (Rugg and Coles, 1995). Of the tasks used to evoke ERPs components, the auditory oddball paradigm is one of the most suited for both experimental and clinical investigation (Squires et al., 1976; Duncan-Johnson and Donchin, 1977; Verleger et al., 1991; Polich et al., 1985; Polich, 1987a, Polich, 1987b, Polich, 2004a, Polich, 1991, Polich, 1996, Polich, 1998, Polich, 2004b; Chapman et al., 2007), since it generates a series of well-characterized components reflecting different stages of auditory processing. In the oddball task, subjects are exposed to a sequence of visual or auditory stimuli in which a small amount (usually 15% or 20%) of deviant stimuli (oddball), differing from standard stimuli, is randomly presented (Polich, 2004a). Subjects may be invited to perform a distracting task and to listen passively to the sequence of standard and deviant stimuli (distracted condition), or to pay attention to the occurrence of deviant stimuli inserted in the sequence of standard stimuli (active condition). In these two conditions target stimuli evoke different sequences of ERP components (Kok, 2000).

Both distracted and active conditions evoke a first negative deflection, named N100, reflecting the activation of the secondary auditory cortex (Picton, 1988; Mangun and Hillyard, 1995). This component, reflecting the obligatory activation of perceptual processes (Picton, 1988), shows an increased amplitude in the active task due to an attention-related facilitator mechanism that increases the amount of sustained resources necessary for processing the incoming stimulus in a task-related manner (Mangun and Hillyard, 1995).

The Mismatch Negativity (MMN – Näätänen et al., 1978, Näätänen et al., 1982; Näätänen, 1992; see Näätänen et al., 2005 for a review), which is evoked both in distracted and active tasks, reflects a comparator mechanism of sensory memory (echoic memory) that automatically and unconsciously stores a short-living non-semantic representation of the physical features of the stimuli (Cowan et al., 1993).

Another negativity, which is greater than MMN, named N2b, is evoked in the active task (Kok, 2000). This latter component overlaps the MMN so that, in the active condition, the MMN is usually masked by the averaging procedure (Pekkonen et al., 1996). The N2b evoked in the active task reflects selective endogenous mechanisms involved in the detection of task-relevant characteristics of targets (Näätänen et al., 1982; Mangun and Hillyard, 1995; Amenedo and Diaz, 1998).

The most extensively studied component evoked by the active oddball task is the parietal P300 or P3b (Kok, 2000; Polich, 2004a). One of the functional rules attributed to this component is the context-updating of mental representation when a deviant stimulus occurs and it matches with the mental representation of the task-relevant stimulus (Donchin, 1987; Polich, 2004b). P300 latency represents the time needed to stimulus categorization and its amplitude seems to be related to the magnitude of the transient attention-related resources recruited for the execution of the task (Kok, 2000).

Therefore, the study of all these components, that can be easily evoked by an ad hoc paradigm, provides a tool usable to define the profile of auditory perceptual, pre-attentive, attention-related and cognitive processes.

Previous results on the effect of aging on these ERP components, obtained by various paradigms and different settings, report that (i) N100 is not affected by age (e.g., Bahramali et al., 1999), at least in the active task (ii) MMN amplitude, but not its latency, decreases with age (Cooper et al., 2006; Pekkonen et al., 1996) (iii) N2b (Amenedo and Diaz, 1998) and P300 latencies increase with age in contrast with their amplitude that decreases along the lifespan (Polich, 1996).

Despite many papers concerning such effects, a complete description of the spectrum of components elicited by the same rare stimulus in both active and distracted tasks in a well-balanced group of normal subjects is lacking.

Therefore, the present study aims at (1) proving that a single simple ad hoc eliciting procedure can be used (i) to investigate age-related variations of ERP components elicited by auditory oddball paradigm in normal people and (ii) to improve insight into the cognitive features of normal aging (Polich, 1998), taking into account gender, education level and task repetition (2) producing normative values usable in clinical practice.

Section snippets

Subjects

A convenient sample of 72 ambulant normal subjects was planned for the study. The sample was balanced so that it should comprise 10–12 subjects in each of the 6 decades of age between 20 and 80 years (20–29, 30–39, 40–49, 50–59, 60–69, 70–80 years), homogeneously distributed for gender in each decade. Four subjects (2 females and 2 male) were subsequently excluded for further analysis because their ERPs showed too many artefacts and/or eye blinks. Therefore, 68 subjects were used for data

Results

Latencies and amplitudes of each component evoked by the rare deviant stimuli were expressed as means ± SD (see Table 2).

The ERPs evoked by the odd or rare tones during the distracted condition in Fz (left) and the active condition in Pz (right) in the 6 decades of age are shown in Fig. 1. The two lines underline the latency of N100 and the P300 in the distracted and active conditions, respectively. Fig. 2 shows the difference between the ERPs evoked by the odds and the frequent stimuli during

Discussion

The effect of age, block repetition, and gender on ERP components evoked by the rare deviant tones both in the distracted and active auditory oddball tasks was described in a well-balanced group of normal subjects. The study confirmed and provided a reliable estimate of the effects of aging on N100 and MMN amplitudes and on N2b and P300 latencies and amplitudes. It proved greater P300 amplitude in females than in males, independently of age, and showed significant prolongation of P300 latency

Disclosure statement

We state that there are no potential conflicts of interest, including any financial, personal or other relationships with people or organizations that could inappropriately influence the current study. The study has been approved by the pertinent Hospital Authority.

Acknowledgements

This research was supported by grant from MIUR and from the University of Padua to Piero Amodio.

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