Impaired preconscious auditory processing and cognitive functions in Alzheimer's disease☆
Introduction
Magnetoencephalography (MEG) is a non-invasive method to study cerebral function with millisecond time resolution (Hämäläinen et al., 1993). Previous MEG studies with normal subjects have demonstrated functional asymmetry in parallel auditory processing, that is, auditory responses peaked slightly earlier in the contralateral than in the ipsilateral auditory cortex with respect to the ear stimulated (Rinne et al., 1999, Pantev et al., 1998, Mäkelä et al., 1993, Pantev et al., 1986, Nakasato et al., 1995). Recent MEG findings have shown that aging and especially Alzheimer's disease (AD) impair parallel preconscious auditory processing between the hemispheres and that this is mainly caused by the delayed cortical processing in the hemisphere ipsilateral to the ear stimulated (Pekkonen et al., 1996, Perret, 1974). In AD, a massive neuronal loss mainly involves hippocampal formation and cortical association areas, the primary auditory cortices being less damaged (Davies et al., 1992, Wechsler, 1978). It has not been studied thoroughly with MEG, however, whether the preconscious auditory processing is abnormal already in AD patients with mild to moderate cognitive symptoms. The second aim of the present study was to investigate whether the damaged preconscious auditory processing correlates with the deterioration of higher cognitive functions in patients with AD.
Section snippets
Material and methods
Eighteen healthy, right-handed subjects (mean age 68 years, range 59–76 years; 8 males) and 22 outpatients with probable AD (mean age 64 years, range 51–80 years; 8 males, one left-handed) participated in the study. After a complete description of the study to the subjects, written informed consent was obtained from each subject or his/her near relative. The study was accepted by the Ethics Committee of the Department of Neurology, the Helsinki University Central Hospital, in compliance with
Results
Fig. 1 demonstrates the magnetic responses of one AD patient and one control subject to the standard tones with the ISI of 2.5 s. Each subject elicited clear P50m and N100m responses, the maximal amplitudes being over the temporal lobes. The patient had larger latency difference between the ipsilateral and contralateral N100m responses than the healthy subject.
The interhemispheric latency differences of the AEFs, which were first calculated and then subjected to group by ISI analysis (repeated
Discussion
Our results provided MEG-evidence for a significant correlation between the delayed preattentive auditory processing in the left hemisphere and impaired language functions in patients with AD. The left hemisphere usually contributes to the language functions when subjects are right-handed as most subjects were in this study (Mayeux and Chun, 1995). Thus both the delayed ipsilateral N100m response and the deteriorated language functions probably reflect functional changes caused by the loss of
Acknowledgements
This work was supported by the Academy of Finland and the EU grant BMH4-CT96-08 19 (COBRAIN) and by the Helsinki University Central Hospital Research Funds.
References (28)
- et al.
Age and Hemisphere effects on dendritic structure
Brain
(1996) - et al.
The effect of age and Alzheimer's disease on pyramidal neuron density in the individual fields of the hippocampal formation
Acta Neuropathol
(1992) - et al.
The Token Test: A sensitive test to detect disturbances in aphasics
Brain
(1962) - et al.
The auditory P50 response is normal in Alzheimer's disease when measured via a paired click paradigm
Electroenceph Clin Neurophysiol
(1994) - et al.
‘Mini-mental status.’ A practical method for grading the cognitive state of patients for the clinician
J Psych Res
(1975) Fuld Object-Memory Evaluation
(1982)- et al.
The middle latency auditory evoked potential may be abnormal in dementia
Neurology
(1992) - et al.
Magnetoencephalography - theory, instrumentation, and applications to non-invasive studies of the working human brain [Review]
Rev Mod Phys
(1993) - et al.
The Boston Naming Test
(1983) Principles of neural science
Auditory function in Alzheimer's disease
Neurology
High-precision neuromagnetic study of the functional organization of the human auditory cortex
Audiol Neurootol
Functional differences between auditory cortices of the two hemispheres revealed by whole-head neuromagnetic recordings
Human Brain Map
Acquired and hereditary dementias
Cited by (36)
Role of Magnetoencephalography in the Early Stages of Alzheimer Disease
2020, Neuroimaging Clinics of North AmericaCitation Excerpt :MEG is a young technique as compared with EEG, and its application to the AD-continuum has been relatively recent. In fact, the first papers devoted to the investigation of AD by means of MEG appeared in the late 1990s.31,32 In the forthcoming pages it will be shown that most of the previously described EEG evidence of electrophysiological changes in AD have been replicated by MEG studies.
Auditory post-processing in a passive listening task is deficient in Alzheimer's disease
2014, Clinical NeurophysiologyCitation Excerpt :Since both the N100 and the P300 amplitude in patients with AD were not different to those measured in the elderly controls, this effect was not due to a general amplitude decrease across all information processing stages in the AD sample. This is supported by the fact that previous studies found no differences in N100 amplitude between elderly controls and AD patients (Golob and Starr, 2000; Lai et al., 2010; Pekkonen et al., 1999). Furthermore, Ford et al. (1997) reported that only the P300 amplitude elicited by an active oddball task was reduced in AD.
Navigated TMS combined with EEG in mild cognitive impairment and Alzheimer's disease: A pilot study
2008, Journal of Neuroscience MethodsEnhanced magnetic auditory steady-state response in early Alzheimer's disease
2006, Clinical Neurophysiology
- ☆
Resubmitted to Clinical Neurophysiology, June 3, 1999.