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Biomedical subjects

D Papakostopoulos

Publications and source records attributed to D Papakostopoulos.

At least 37 records · Page 2Linked to original sources
PubMed1985

Neurophysiological correlates of psychomotor activity in chronic schizophrenics.

The movement-related brain macropotentials (MRBMs) of 13 chronic schizophrenics (7 paranoid and 6 hebephrenic) were recorded during a motor perceptual task and compared to those of 13 normal subjects matched by age, sex and IQ. The cerebral activity was recorded from Fpz, Fz, Cz, Pz, and right and left precentral areas and the electromyographic activities from the left and right forearm flexor muscle groups. Analysis of variance was performed to test the correlation between the MRBMs and groups, sets and performances. The results indicate that the performance considered in tests of 'performance time,' as 'performance shift' and as number of 'target performances' was poorer in chronic schizophrenics than it was in the control group. In parallel with the performance, the MRBMs of chronic schizophrenics were also significantly different in comparison to the normal subjects. In particular, the BP amplitude was reduced in all areas; the MCP and P200 were also abnormally reduced. The SPP was present but it had a small amplitude in the parietal region. These differences in chronic schizophrenics could be explained as multidimensional biopsychological deficits: the disturbed performance is the result of impairment in developing appropriate changes of set, defective inhibition of sensory information, and reduced utilization of the outcome data.

Adolescent↗
PubMed1984

Combined electrophysiological assessment of the visual system in central serous retinopathy.

Six subjects suffering from idiopathic central serous retinopathy were examined during the acute phase using a battery of neurophysiological tests. The records (using skin electrodes) included the electro-oculogram (EOG), the white light electroretinogram (ERG) during various stages of dark and light adaptation, and the flash and pattern reversal visual evoked potentials. Results obtained from the affected eye were compared with those from the healthy eye. The values of the healthy eye were not significantly different from our normal control group. The EOGs of the affected eyes were not significantly different from those of the healthy eyes. The 'a' wave of the ERG during light adaptation was significantly (P less than 0.05) smaller in the affected eye. The amplitudes of the other components and the latencies of all components were not affected. The latency of the PR-VEP of the affected eye in all subjects was prolonged in comparison with the unaffected eye. In 3 subjects the latency was prolonged by more than 2 S.D.s compared with our control group. The amplitude of the PR-VEP in 5 of our 6 subjects was slightly but significantly (P less than 0.02) smaller in the affected eye. There was no correlation between amplitude and latency changes.

Adaptation, Physiological↗
PubMed1983

Movement-related brain macropotentials during skilled performances. A developmental study.

A developmental study of movement-related brain macropotentials (MRBMs) during a self-paced bimanual skilled performance task (Papakostopoulos 1980) was carried out. MRBMs were obtained from Fpz, Cz and right and left pre-central and electromyograms were recorded from the left and right flexor muscles of the forearms in 30 normal children ranging from 8 to 13 years of age. A consistent Bereitschaftspotential appeared in children of 10 years; in the younger children it was absent or it was positive at precentral and central locations. The motor cortex potential and P200 were present in all children. The skilled performance positivity (SPP), absent at 8 and 9 years, appeared at 11 years of age and was present in older children. The latency of P200 and SPP decreased with age. ANOVA tests showed a statistically significant age effect on performance, EMG rise time and MRBMs; MRBMs were not statistically influenced by time in the experiment: MCP and P200 increased in amplitude with improvement of performance. The results indicate different rates of maturation of the neuronal systems underlying the genesis of the various movement-related brain macropotentials.

Adolescent↗
PubMed1980

A no-stimulus, no-response, event-related potential of the human cortex.

Brain macropotentials related to self-paced uni- or bimanual, unskilled or skilled movements were recorded from the motosensory cortical areas from 26 subjects. EMG of the active muscles, respiration, GSR, ECG and potentials generated by eye movements were also recorded. Subjects triggered the sweep of an oscilloscope with self-paced thumb movements in the following, unskilled, conditions: left-hand press (LHP), right-hand press (RHP), pressing with both hands simultaneously. They then performed a skilled performance task (SPT) during which the sweep was initiated by an LHP and was terminated within 40--60 msec by an RHP. Ten of the tested subjects participated in a variation of the skilled performance task during which no visual feedback was provided about their performance. All movements were preceded by sustained negativities known as N, component or Bereitschaftspotential (BP). All actions were followed by the motor cortex potential (MCP) with a latency of 32 msec from the EMG peak and a positivity with a latency of 200 msec from movement execution and initiation of the oscilloscope trace. Only the movements during SPT were followed by an additional positivity with a latency of 460 msec from the movement, having a centroparietal distribution and a mean amplitude at the vertex of 12.7 muV and S.D. of 5.0 muV. This skilled performance positivity (SPP) was independent of the amplitude of the previous BP and MCP and it was absent when the subject executed a variation of the SPT test during which visual feedback was not provided. Thus the SPP potential seems to be independent of stimulus or response characteristics and develops under experimental circumstances in which the subject expects and receives information about the outcome of coordinated self-placed movements.

Adult↗
PubMed1977

Cortical potentials associated with the detection of visual events.

A positive-going potential, which reaches a maximum at the vertex and midline parietal scalp electrodes, occurs in the human being when an infrequent, significant event occurs in a continuously observed visual display. It is not time locked to eye movements or operant response and appears to be generated when the observer recognizes an event that he has been instructed to detect.

Cerebral Cortex↗
PubMed1976

Causes of initial visual loss following blunt ocular injuries: an experimental study.

We have investigated in anaesthetised pigs the electrical responses of the retina to light after blunt injuries to the eye. Retinograms, cortical visual evoked responses and intraocular pressures were recorded before and after non-perforating mechanical trauma of sufficient severity to produce traumatic retinal opacification. After injury, applanation pressures rose up to 34 mm. Hg above normal, reaching peak values 4 to 12 minutes after trauma and returning to pre-trauma levels after about 45 minutes. These pressure changes were not responsible for the immediate abolition of the B wave of the retinogram or of the cortical visual evoked responses which occurred after trauma, but increases of intraocular pressure modified the recovery pattern of the visual evoked response.

Animals↗