Standard auditory evoked potentials (AEP) were recorded in 50 schizophrenic patients and 47 normal controls. All patients were rated on the Brief Psychiatric Rating Scale (BPRS), the Scale for the Assessment of Negative Symptoms (SANS), the Scale for the Assessment of Positive Symptoms (SAPS), and the Positive and Negative Syndrome Scale (PANSS), and were classified in three groups (positive-type [n = 10], negative-type [n = 23]and mixed-type [n = 17]patients) according to the normative criteria suggested by Kay. The mean latencies of AEP components (N1, P2, N2) and mean peak-to-peak amplitudes (N1P2, P2N2) did not correlate with age, duration of illness, length of hospitalisation or neuroleptic dosage. The evoked response did not differ between the three groups of patients (positive, negative and mixed). There was only a trend (P = 0.075) to a longer N1 latency in the negative-type group and a shorter one in the positive-type group than in the mixed-type and the control groups. The latency of N1 component correlated significantly with negative symptoms of schizophrenia (SANS scores). This correlation was related to the severity of a depressive dimension of the disorder reflected by the “depressive factor” of BPRS or “affective flattening” and “avolition” subscales of SANS.

Visually evoked field potentials in human subjects and single-cell responses from retinal ganglion cells in the macaque monkey were compared in closely similar stimulus situations. The classical heterochromatic flicker photometry (HFP) technique was used to measure spectral sensitivity in man, both psychophysically and by recording the 40-Hz response, and to measure the spectral sensitivity of magnocellular (MC-) pathway cells of the macaque. The three measures gave closely similar spectral-sensitivity curves. Close agreement between the three measures was also found when the variable-modulation HFP technique was used to measure spectral sensitivity. When the relative phase between red and green lights was varied, the point of minimum subjective flicker for human observers was close to a sharp minimum found in the amplitude of the 40-Hz response in human and was also close to a minimum in the response of MC-pathway neurons in the monkey. The human 40-Hz response saturated at between 10 and 30% modulation depth, and so did the response of MC-pathway cells in the monkey.

The 16-Hz response in human showed none of the above correlations with MC-pathway properties. On the other hand, parvocellular (PC-) pathway cells responded vigorously to constant-luminance, chromatic modulation, at frequencies higher than can be detected by human observers. The human 16-Hz response also was strong in that stimulus situation. In addition, the response of PC-pathway cells on increasing modulation depth showed little saturation, and this behaviour was paralleled by the human 16-Hz response.

We conclude that the properties of MC-pathway neurons in macaque are closely similar to the properties of the human 40-Hz response in the respects just described. We suggest that the 40-Hz response may offer a means of objectively isolating and investigating the contribution of the magnocellular stream to cortical activity in human. In contrast, the properties of PC-pathway neurons in macaque are quite different from the properties of the human 40-Hz response, and in several respects resemble the properties of the human 16-Hz response.

Albino rats have recently been reported to have increment thresholds against dim backgrounds that are two log units higher than those of pigmented rats. We, on the other hand, have failed to confirm these differences using electroretinogram b waves and pupillary light reflexes. This paper reports on experiments using evoked potentials from cortex and colliculus and single-unit recordings from colliculus.

We recorded visual-evoked potentials from cortex and superior colliculus in the strains of albino (CD) and pigmented (Long-Evans) rats used in the earlier studies. Thresholds were determined on eight fully dark-adapted animals by extrapolating intensity-response curves to the point at which there was zero evoked potential. The average dark-adapted threshold for the visual-evoked cortical potential was —5.26 log cd/m2in pigmented and —5.80 log cd/m2 in albino animals. The average dark-adapted threshold for the superior colliculus evoked response was —5.54 log cd/m2 in pigmented and —5.84 log cd/m2 in albinos. The differences were not statistically significant. On the same apparatus, the average absolute threshold for three human observers was —5.3 log cd/m2, a value close to the rat dark-adapted thresholds. Thus, visual-evoked cortical potentials and superior collicular evoked potentials failed to confirm the report of higher dark-adapted thresholds for albinos. In addition, we find that single units in superior colliculus in the albino rat respond to very dim flashes.

We have estimated the absolute threshold of congenic albino and pigmented mice (C57) using ERG, pupillary light reflex, and VHP. We are unable to detect strain differences using ERGs or VEPs, but pupillary thresholds appear to be different. In addition, as we have previously reported for rats, VEP thresholds are considerably lower than the ERG b−wave thresholds. The VEP thresholds agree with behavioral data from pigmented mice made by others. The mouse VEP thresholds are close to the VEP thresholds in rats and the psychophysical thresholds of two human observers.

Disturbances in processing simple acoustic changes in a stream of stimuli have been widely reported in patients with schizophrenia, but little is know about auditory feature conjunction in these individuals. This study was designed to examine the extent to which patients with schizophrenia automatically process changes in conjunction of auditory features by using event-related brain potentials. Seventeen patients and 17 age-matched controls were presented with frequent low pitch tones at 45° to the left of center and frequent high pitch tones at 45° to the right of center while performing a continuous visual serial-choice reaction time task. The sequence of auditory stimuli included rare conjunction-deviants comprised of a different combination of features (e.g., low pitch tone at 45° right) and double-deviant tones that differed from the standard tones in both pitch and location (i.e., middle pitch at 0° azimuth). Conjunction-deviant stimuli elicited an MMN wave that was maximum at frontocentral sites. Compared with controls, the MMN to conjunction-deviant was reduced in patients and was more centrally distributed. Double-deviant sounds generated a biphasic MMN followed by a P3a wave at central sites. Both MMN and P3a were reduced in patients compared with controls. These results show that patients with schizophrenia have difficulty in automatically detecting changes in a combination of auditory features as well as orienting to what “normally” would be considered salient by healthy individuals.

Recognition potential (RP), a recently discovered electrophysiological response of the brain, is sensitive to semantic aspects of stimuli. Given its peak values (about 250 ms), RP may be a good candidate for the study of semantic processing during its occurrence. However, its topography and neural generators are largely unknown. To improve this state of affairs, high-resolution electroencephalography and brain electrical source analysis were carried out. Results suggest a possible origin of RP in the lingual gyrus, hence reflecting the activity of the basal extrastriate areas. RP therefore appears to be a highly valuable tool in the study of those regions considered to be the “third language areas” (in addition to Broca's and Wernicke's areas), whose precise role in language processing is still largely unknown. Another important finding was that RP amplitude in the left hemisphere differed as a function of the semantic category of the stimuli, providing evidence for the sensitivity of this component to semantic categorization. A tentative proposal is made with regard to the role of the basal extrastriate areas.

This study investigated the relationship between resistive load magnitude, load magnitude estimation, and the respiratory-related evoked potential. In Part 1, 10 healthy subjects estimated the magnitude of five inspiratory resistive loads. Two subjects were shown to have a markedly reduced slope of the magnitude estimation-resistive load relationship and were suggested to be “poor perceivers” of respiratory stimuli. In Part 2, evoked potentials were recorded from the same 10 subjects using the same resistive loads as Part 1. A log-log plot of the group averaged P1 amplitudes showed a linear relationship with resistive load. Aberrant P3 components were seen in the 2 poor perceiving subjects and one of the 2 showed no late response. In the other 8 subjects, P3 varied as a function of resistive load, being augmented to larger loads. These results provide evidence that P3 may be a key index of the perception of respiratory sensitivity and effort.