Pattern of P50 suppression deficit in patients with epilepsy and individuals with schizophrenia

OBJECTIVE: To identify P50 suppression in patients with epilepsy, to investigate the effect of seizure control on P50 suppression, and to compare epilepsy patients with individuals with schizophrenia and healthy volunteers. METHOD: P50 evoked potential parameters and P50 suppression were studied crossectionally in patients with uncontrolled or controlled epilepsy, in individuals with schizophrenia and in healthy volunteers. RESULTS: Individuals with schizophrenia had significantly smaller conditioning stimulus (S1) amplitude, and patients with epilepsy had larger test stimulus (S2) amplitude. Mean S2/S1 ratio was 0.71±0.33 for patients with uncontrolled epilepsy; 0.68±0.36 for patients with controlled epilepsy; 0.96±0.47 for individuals with schizophrenia, and 0.42±0.24 for healthy volunteers. CONCLUSION: The sensory filter of patients with epilepsy is altered, and this alteration is not associated with seizure control. Also, it works differently from the sensory filter of individuals with schizophrenia.

Modulation of Calcium-Dependent Postsynaptic Depression Contributes to an Adaptive Sensory Filter

Bastian, Joseph. Modulation of calcium-dependent postsynaptic depression contributes to an adaptive sensory filter. J. Neurophysiol. 80: 3352–3355, 1998. The ability of organisms to ignore unimportant patterns of sensory input may be as critical as the ability to attend to those that are behaviorally relevant. Mechanisms used to reject irrelevant inputs range from peripheral filters, which allow only restricted portions of the spectrum of possible inputs to pass, to higher-level processes, which actively select stimuli to be “attended to.” Recent studies of several lower vertebrates demonstrate the presence of adaptive sensory filters, which “learn,” with a time course of a few minutes, to cancel predictable patterns of sensory input without compromising responses to novel stimuli. Predictable stimuli include “reafferent” stimuli, which occur as a result of an animal's own activity, as well as stimuli that are simply repetitive. The adaptive characteristic of these filters depends on an anti-Hebbian form of synaptic plasticity that modulates the strength of multisensory dendritic inputs resulting in the genesis of “negative image” signals, which cancel the predicted pattern of sensory afference. This report provides evidence that the mechanism underlying the anti-Hebbian plasticity involves the modulation of a calcium-dependent form of postsynaptic depression.

The Sensory Filter in Schizophrenia: A Study of Habituation, Arousal, and the Dopamine Hypothesis

SummaryThe possible failure of a notional sensory filter in schizophrenia was studied by means of habituation of the orienting response. Non-paranoid schizophrenics failed to habituate, but paranoids habituated normally. Paranoids, however, showed a different impairment: they responded to a dishabituating tone as if the novel stimulus were somewhat familiar.The failure of habituation in non-paranoids could not be explained in terms of arousal when the index was the rate of skin conductance fluctuation. Neurotic controls showed considerably higher levels than either group of schizophrenics.Non-paranoid schizophrenics had lost the normal inverse relationship between habituation and level of arousal as manifested in the rate of spontaneous skin conductance fluctuation.

A Physiological Difference Between Hallucinosis and Schizophrenia

Boulton (1971), in an authoritative review, has pointed out that biochemical research into schizophrenia has depended upon the assumption that hallucinogens, such as mescaline and LSD produce a state similar to schizophrenia, and that such research has therefore principally been concerned with attempts to find hallucinogens, or substances closely related to them, in the bodily fluids of schizophrenics. Since this model has been criticized on phenomenological grounds, we decided to make a comparison between states of visual hallucinosis and of schizophrenia with thought disorder, using a measure which tests a common hypothesis concerning the origin of schizophrenic symptoms. This hypothesis suggests that the symptoms of schizophrenia are manifestations of failure of a hypothetical sensory ‘filter’ (Broadbent, 1958). This mechanism determines the individual's ‘selective inattention’ to the irrelevancies of his environment. Its function can be assessed by a study of habituation, which is the process whereby a randomly repeated stimulus fails in time to elicit an orienting response.