We describe a programmable multi-chip VLSI neuronal system that can be used for exploring spike-based information processing models. The system consists of a silicon retina, a PIC microcontroller, and a transceiver chip whose integrate-and-fire neurons are connected in a soft winner-take-all architecture. The circuit on this multi-neuron chip approximates a cortical microcircuit. The neurons can be configured for different computational properties by the virtual connections of a selected set of pixels on the silicon retina. The virtual wiring between the different chips is effected by an event-driven communication protocol that uses asynchronous digital pulses, similar to spikes in a neuronal system. We used the multi-chip spike-based system to synthesize orientation-tuned neurons using both a feedforward model and a feedback model. The performance of our analog hardware spiking model matched the experimental observations and digital simulations of continuous-valued neurons. The multi-chip VLSI system has advantages over computer neuronal models in that it is real-time, and the computational time does not scale with the size of the neuronal network.

Action Potentials↗

PubMedDate not supplied

A silicon neuron.

By combining neurophysiological principles with silicon engineering, we have produced an analog integrated circuit with the functional characteristics of real nerve cells. Because the physics underlying the conductivity of silicon devices and biological membranes is similar, the 'silicon neuron' is able to emulate efficiently the ion currents that cause nerve impulses and control the dynamics of their discharge. It operates in real-time and consumes little power, and many 'neurons' can be fabricated on a single silicon chip. The silicon neuron represents a step towards constructing artificial nervous systems that use more realistic principles of neuronal computation than do existing electronic neuronal networks.

Animals↗

PubMedDate not supplied

The Jk(a-b-) phenotype in New Zealand Polynesians.

The Kidd locus phenotype Jk(a-b-) was detected in 0.9 percent of Polynesians living in New Zealand. Over a period of 13 years, nine examples of anti-Jk3 were detected, one of which caused a delayed hemolytic transfusion reaction. Other examples resulted in mild hemolytic disease of the newborn. The anti-Jk3 reacted as an inseparable antibody, confirmed that inheritance of the Jk(a-b-) phenotype was best explained by the presence of a silent Jk allele.

Alleles↗

PubMedDate not supplied

The difficult crossmatch: a consideration of the staff and not the method.

The crossmatching laboratory is regarded as a stressful work environment where many nontechnical issues may influence the interpretation of test results, particularly if the results are unclear. An attempt has been made to identify major areas of conflict and stress and to demonstrate their relationship to the quality of crossmatching. The Janis an Mann model for decision making in conflict situations is presented and related to interpretation of crossmatches.

Blood Grouping and Crossmatching↗

PubMedDate not supplied

Performance of the indirect antiglobulin test does not show a circadian rhythm.

Performance of the indirect antiglobulin test by workers in a blood bank was examined for signs of a rhythmical relationship between the time of day and the frequency of error. All participants were experienced in blood group serology and completed sets of 12 antiglobulin tests at 4-hour intervals over a 24-hour period. Ten of the original 17 participants repeated the experiment after an interval of 7 months. About 50 percent of participants made more errors in the daytime or the nighttime in each experiment; however, these groups were unstable and contained different individuals in each experiment. Significant (p less than or equal to 0.05) time-related cosinor rhythms could be demonstrated for four individuals in one experiment, but this finding was not reproduced in a second experiment. There was no indication that the amount of sleep deprivation which occurred had a significant influence on the investigation, and the individual frequencies of error at 0800 hours appeared to be a stable individual characteristic. The results highlight the importance of examining workplace-related performance as an individual rather than a group phenomenon.

Blood Grouping and Crossmatching↗

PubMedDate not supplied

Some quantitative aspects of the human monocyte erythrophagocytosis and rosette assays.

The sensitivity of peripheral blood mononuclear phagocytes (PBMPs) in the red cell (RBC) adherence and erythrophagocytosis assays were investigated using anti-D of subclasses IgG1 and IgG3. Particular emphasis was placed on identifying variability between PBMP preparations from different healthy donors. About 500 molecules of IgG1 type anti-D per RBC and about 100 molecules of IgG3 antibody per RBC were the lowest levels of sensitization which elicited a weak, positive test. Considerable variation between different preparations was seen, and it appeared that the capability of a PBMP preparation to react with weakly sensitized RBCs may not be closely related to its strength of reaction with strongly sensitized cells. PBMPs which were recovered after storage in liquid nitrogen were more reactive in both assays than freshly prepared PBMPs from the same donor. This study demonstrated the importance of weakly sensitized RBCs as part of the control system and indicated a need for caution when establishing a negative test result when the clinical significance of RBC antibody is being investigated.

Blood Preservation↗