Impaired early visual processing in disorganised schizophrenia.

Topographic differences in flash/pattern shift VEP data are evaluated in paranoid (n: 38), disorganized (n: 23) and residual (n: 23) schizophrenic subtypes and compared to normal controls. Increased early P1 and a restricted diffusion of the late P2 responses suggest dopaminergic over- and cholinergic underactivity in paranoid and residual schizophrenia. A distinctive pattern N145 reflects well-preserved attentional resources in the paranoid subtype. Latency increase and amplitude decrease of the pattern N145 concur with abnormal antisaccades documented in disorganized behaviour. VEP-data might help differentiate between schizophrenic subtypes.

Facilitation of early and masking of late cortical responses in dementia.

Topographic differences in longlatency SSEP and flash VEP data are compared in 3 different psychiatric patient groups. Differences between schizophrenia and affective disorder are restricted to somatosensory P100 amplitude gradients along the antero-posterior axis. In contrast EP-differences between psychiatric patients and dementia are prominent, encompassing both late and early (< 100 ms) responses. Our flash P 2 and somatosensory P 3 data are in accordance with previous findings. Multi-modal positive responses with a latency of 40-80 ms are significantly increased in dementia. This facilitation suggests cortical dysfunction and/or subcortical gating impairment.

Auditory information processing in schizophrenia.

Early N1P2 and late N2P3 responses generated in an auditory oddball paradigm are topographically compared in three psychiatric patient groups. In schizophrenia N1 and N2 amplitude is comparable with dementia and significantly decreased with respect to affective disorder. In contrast, P3 amplitude does not allow discriminating schizophrenia from affective disorder but is significantly diminished in dementia. The late N2P3 response shows a topographic effect along the fronto-occipital axis. Schizophrenia is characterized by an iCNV and N2 maximum over the frontal planes and a compound P3 lacking distinct frontal and parietal components. The findings are discussed in reference to literature data and current hypotheses/theories concerning information processing. Our findings favour an important dysfunction of automatic processing including early selection in schizophrenia.

Auditory vertex potential in children: a cognitive hypothesis.

In children the early N1P2 response generated by an auditory oddball paradigm is a compound negative potential with distinctive 165-ms temporal and 240-ms frontocentral components. As this configuration differs considerably from the adult response, it may be assumed that neural systems engaged in auditory attentional processes differ with age. It is argued that the auditory vertex potential might index frontal lobe development and matching mechanisms. In combination with EEG spectral data this cognitive parameter could initiate an alternative approach to the evaluation and research of learning and attention deficit disorders.

Sleep and the temporal lobe.

The main interest in the association between sleep and temporal lobe dysfunction is based on the activation of ictal and interictal epileptic phenomena. The clinical semiology of NREM and REM parasomnias may resemble complex partial seizures. The differentiation between epilepsy and dissociated states of wakefulness and sleep is of high diagnostic and therapeutic importance. Systems within temporal lobe structures are also responsible for disturbed sleep or dyssomnia. The limbic brain is connected with different nodal points in the network underlying sleep organisation and participates in both sleepinducing and arousal mechanisms. Experimental amygdala kindling, an animal epilepsy model involving temporal structures, induces disturbed sleep patterns favouring waking and light sleep. In epilepsy unstable disrupted and superficial sleep patterns prevail without overt seizures. Sleep-fragmentation and deprivation may impair daytime functioning and cognitive performance by lowering the seizure-threshold. The recognition of dyssomnia and of excessive sleepfragmentation and sleepiness has obvious implications for behavioural and drug treatment.

Psychological and neurophysiological dysfunctioning during wakefulness in narcolepsy.

Memory complaints and altered states of consciousness with automatic behaviour of narcoleptic patients indicate cognitive dysfunctioning. Although more problems arise while performing attention tasks than memory tasks, the neuropsychological test inquiry doesn't indicate one particular neuropsychological function as consistently impaired. They often perform well because they compensate impaired wakefulness by an increased willingness to respond. Neurophysiological research indicates that the sometimes occurring cognitive dysfunction is associated with a waxing and waning between wakefulness and sleep. The increased psychopathology is partly a reflection of, partly a reaction to the symptoms. The impact of hypersomnia on psychosocial functioning is more important than that of epilepsy in epileptics. In severe cases smoking and driving should better be dissuaded.