Biomedical subjects

Ian M Colrain

Publications and source records attributed to Ian M Colrain.

21 records · Page 2Linked to original sources

PubMed2002

An examination of evoked K-complex amplitude and frequency of occurrence in the elderly.

The elderly consistently display lower levels of slow wave sleep (SWS), primarily because of the small amplitude of their delta activity. Given that delta electroencephalogram (EEG) and K-complexes are thought to be generated by the same mechanisms, it was hypothesized that K-complex amplitude and rate of production would be lower in the elderly. K-complex amplitude was assessed by averaging K-complex responses to auditory stimuli, and measuring the amplitude of the N550 component of the averaged evoked response. Ten young (five males and five females; mean age 23.10 +/- 5.36 years) and 10 elderly adults (six males and four females; mean age=75.60 +/- 4.48 years) who were neurologically healthy and free from medication spent two non-consecutive nights in the sleep laboratory. EEG was recorded from six gold plate electrodes (Fz, Fcz, Cz, Cpz, Pz and O2) referenced to A1 + A2. Tone clicks (1000 Hz), of varying intensity from 70 to 100 decibels above measured awake detection threshold, were presented binaurally during stage 2 sleep. Responses were classified according to whether they produced: a K-complex, a vertex sharp wave (VSW), both of these responses or neither response. They were then averaged separately for each response type. The elderly showed a substantially smaller N350 (averaged VSWs) and N550 amplitudes compared with the young subjects. The elderly also showed an augmented but delayed P2 component, followed by a long-lasting positive EEG shift. The smaller amplitude of the averaged K-complex N550 component is consistent with lower delta amplitudes previously reported in the elderly and with the hypothesis that K-complexes and delta activity share the same generator mechanisms. The enhanced P2 component and the long-lasting positive deflection in the EEG in the elderly indicate the existence of age differences other than smaller EEG amplitude.

Adult↗

PubMed2002

The effects of alcoholism on auditory evoked potentials during sleep.

Normal aging is associated with a reduction in the probability that an auditory stimulus will evoke a K-complex during sleep. Additional concomitants of aging are a reduction in the amplitude of the K-complex-related N550, an augmentation of the P2 component and the appearance of a long-lasting positivity (LLP) in the auditory evoked potential. Normal aging is also associated with a dramatic reduction in slow wave sleep (SWS) and a reduction in the volume of cortical gray matter, particularly in the frontal and prefrontal regions of the brain. As in aging, alcoholism is associated with reductions in both cortical gray matter and SWS. It can, therefore, be hypothesized that alcoholics would show similar evoked potential changes to those seen in aging. To test this hypothesis, we studied seven middle-aged abstinent long-term alcoholics and eight age-matched normal controls. Each subject spent one night in the laboratory. Electroencephalogram (EEG) was recorded from six midline scalp sites and auditory stimuli were presented during stage 2 non-rapid eye movement sleep. N550 amplitude in the K-complex average was lower in the alcoholics as compared with controls as was the likelihood of K-complex production. No differences were noted in either amplitude or latency of the P2 or N350 components, and both groups displayed a prominent LLP potential. The pattern of reduced K-complex production and N550 amplitude in alcoholics as compared with age-matched controls is consistent with an hypothesized association between atrophy of the frontal lobes and reductions in SWS and K-complexes. The finding also suggests that the evoked K-complex may be a relatively simple measure of the effect of alcoholism on EEG during sleep.

Alcoholism↗

PubMed2002

Increased production of evoked and spontaneous K-complexes following a night of fragmented sleep.

STUDY OBJECTIVES: To determine whether K-complex production is better interpreted as being an arousal response or reflective of a sleep protective micro-state. DESIGN: A 3-night study--night 1 as a baseline night, night 2 as a sleep fragmentation night, followed immediately by night 3 as a recovery night. On nights 1 and 3, approximately 400 auditory stimuli were presented during nonREM sleep in the first two sleep cycles, using stimulus parameters previously found to be optimal for K-complex production. SETTING: The sleep research laboratory at the University of Melbourne. PARTICIPANTS: Six young healthy subjects (3 female). INTERVENTIONS: One night of sleep fragmentation. Ten-second auditory tones of up to 110 dB were presented throughout the entire night at approximately 1-minute intervals. MEASUREMENTS AND RESULTS: Sleep drive was increased on the recovery night, as indicated by increased amounts of slow wave sleep, increased sleep efficiency, and a reduction in stimulus-related alpha activity. The incidence of both evoked and spontaneous K-complexes increased significantly on the recovery night. When K-complex trials were averaged, neither N550 (Fz) amplitude nor latency differed between the 2 nights. When vertex sharp waves were averaged, N350 (Cz) amplitude was increased significantly on the recovery night. CONCLUSIONS: The increase in K-complex frequency together with the decrease seen in stimulus-related alpha activity supports the view that they reflect a sleep maintenance, rather than an arousal, response.

Adult↗