Showing papers by "Anton M.L. Coenen published in 2005"

Evolving Concepts on the Pathophysiology of Absence Seizures: The Cortical Focus Theory

Abstract: Four main theories on the pathophysiology of generalized absence seizures have been proposed. The "centrencephalic" theory, proposed in 1954, suggested that discharges originate from a deep-seated diffusely projecting subcortical pacemaker in the midline thalamus. This concept was refined in 1991 with the "thalamic clock" theory, implying that the reticular thalamic nucleus contains the pacemaker cells for the thalamic clock, imposing its rhythm to the cortex. According to other investigators, however, the cortex seems to play a leading role. They suggested that spike-wave discharges have a focal onset in the cortex and are generalized through a rapid propagation. In the "corticoreticular" theory, postulated in 1968, spike-wave discharges are linked to the thalamocortical mechanisms that generate spindles. Rhythmic spindle oscillations generated in the thalamus are transformed into spike-wave discharges when the cortex is hyperexcitable. A 2002 study confirmed in epileptic rats that a functionally intact thalamocortical network is required for the generation of spike-wave discharges. The corticothalamic interrelationships were investigated by means of nonlinear association signal analyses of multiple spike-wave discharges. This showed a consistent focus within the perioral region of the somatosensory cortex. From this focus, seizure activity generalizes rapidly over the cortex. During the first cycles of the seizure the cortex drives the thalamus, while thereafter cortex and thalamus drive each other, thus amplifying and maintaining the rhythmic discharge. In this way the "cortical focus" theory for generalized absence epilepsy bridges cortical and thalamic theories.

Diurnal spectral EEG fluctuations in narcoleptic patients during rest and reaction time tasks

Abstract: Narcolepsy is associated with lowered vigilance. Diurnal variation in vigilance appears altered, but the exact nature of this change is unclear. It was hypothesized that the homeostatic sleep drive is increased in narcolepsy. Decreased levels of vigilance are reflected in low frequency band power in the electroencephalogram (EEG), so these frequencies were expected to be increased in the narcolepsy group. Furthermore, it was expected that low frequency power should increase over the day. Narcoleptic patients and healthy controls participated (36 participants in total); they were not allowed to take medication or naps on the experimental day. EEG was measured at 9:00, 11:00, 13:00, 15:00, and 17:00 hours, during rest and during reaction time tasks. In the narcolepsy group, alpha power was lower at rest at all times. Delta and theta power during rest and task performance increased steadily over the day in this group, from 11:00 hours onwards. Additionally, in the narcolepsy group beta1 and beta2 power during rest appeared increased at the end of the day. The effects in the lower frequency bands strongly suggest that vigilance is low at all times. The progressive increase in low frequency power indicates that the sleep drive is enhanced. It is not clear whether this pattern reflects an extreme state of low vigilance, or a pathological brain condition. The effects in the higher frequencies suggest that narcoleptic patients may make an effort to counteract their low vigilance level.

Animal consciousness and euthanasia: chicken euthanasia in the two-phase stunning system.

Abstract: A form of consciousness cannot be excluded for animals and this has important ethical implications for acceptable slaughter methods, which should result in minimal signs of agitation and distress in the period before unconsciousness is reached. Simultaneous EEG, ECG and behavioural responses were recorded in birds exposed to either two-phase (40% CO2, 30% O2, 30% N2 for 1 min followed by 80% CO2, 5% O2, 15% N2) or single-phase (30% CO2, 60% N2 with <2% O2) controlled atmosphere stunning in a pilot scale system. The EEG traces of birds in the carbon dioxide/nitrogen condition showed many more movement artefacts reflecting wing flaps and strong body movements such as convulsions, and this was confirmed by behavioural observations. These occurred during the period that consciousness could not be excluded; the time till unequivocal unconsciousness (expressed in an iso-electric EEG pattern) was estimated to be 20-50 seconds in the carbon dioxide/nitrogen atmosphere and 50-60 seconds in the carbon dioxide/oxygen/nitrogen condition. In addition, intense and long lasting artefacts in the ECG traces were visible in the carbon dioxide/nitrogen condition but were completely absent in the two-phase condition. These are thought to indicate strong isometric muscle contractions which may be painful and distressing. Time to death was established as heart rate under 180 beats per minute and was around 80 seconds in the carbon dioxide/nitrogen condition and 190 seconds in the carbon dioxide/oxygen/nitrogen condition. The chickens reached unconsciousness slower and died significantly later in the two-phase condition, as judged by the EEG, heart rate and behaviour. However, in the absence of oxygen leading to a faster death, the birds showed strong signs of agitation and distress. We are convinced that a milder death, which takes longer, is to be preferred to a quicker but more distressing death.

Where is the classic interference theory for sleep and memory

Abstract: Walkers target article proposes a refinement of the well known two-stage model of memory formation to explain the positive effects of sleep on consolidation. After a first stage in which a labile memory representation is formed, a further stabilisation of the memory trace takes place in the second stage. which is dependent on (REM) sleep. Walker has refined the latter stage into a stage in which a consolidation-based enhancement occurs. It is not completely clear what consolidation-based enhancement implies and how it can be dissociated from a stage for memory-stabilisation. A more serious consideration, however, is whether a second stage in memory consolidation that is solely dependent on sleep is really necessary. The classical, passive, interference theory is able to explain adequately the findings related to the effects of sleep and memory, and can lead perhaps better to an understanding of the highly variable data in this field.