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S P Heinrich

Publications and source records attributed to S P Heinrich.

7 recordsLinked to original sources
PubMed2001

Coupling of neural activity and BOLD fMRI response: new insights by combination of fMRI and VEP experiments in transition from single events to continuous stimulation.

Functional magnetic resonance imaging (fMRI) measures the correlation between the fMRI response and stimulus properties. A linear relationship between neural activity and fMRI response is commonly assumed. However, the response to repetitive stimulation cannot be explained by a simple superposition of single-event responses. This might be due to neural adaptation or the hemodynamic changes underlying the fMRI BOLD response. To assess the influence of adaptation, the BOLD responses and visual evoked potentials (VEPs) to identical stimuli were recorded. To achieve different adaptation levels, 2-s stimulus epochs alternated with different interstimulus intervals (ISI = 0.0, 0.4, 0.8, 2.0, and 12 s) were presented. Neural adaptation during the checkerboard reversal paradigm used for fMRI measurements is demonstrated. Even if the measured VEP amplitude is used as the weighting function for a linear model, the measured BOLD fMRI signal time-course is not adequately predicted.

Adult↗
PubMed2001

Adaptation dynamics in pattern-reversal visual evoked potentials.

Recording a VEP usually involves prolonged repetitions of the stimulus, but the influence of adaptation is rarely discussed in this context. Two experiments were performed. In Experiment 1 the time course of the response amplitude during steady-state stimulation was assessed. During the first seconds of stimulation we found an increase in amplitude, followed by a continuous exponential decline. This confirmed earlier results. There is considerable inter-subject variability concerning all aspects of the time course in our 19 subjects. Experiment 2 used two types of transient pattern reversal stimuli: one regular stimulus as used in standard clinical applications and one with a pause in between each reversal. N1 and P1 amplitudes did not show significant differential effects. N2 amplitude was reduced by 73% in the standard condition whereas P1 peak time increased slightly but significantly (3.2 ms).

Adaptation, Ocular↗
PubMed2000

Parallel detection of orientation differences in the presence of orientation gradients.

We measured thresholds and reaction times for detecting a target, defined by orientation contrast, as a function of the number of elements displayed simultaneously and of the linear orientation gradient present in the display. This test served to evaluate how well the human visual system is able to ignore smooth gradients in orientation - similar to what it does with gradients of luminance or wavelength. Smooth orientation gradients are common in natural environments as opposed to the usual laboratory (search) experiments. It turns out that targets defined by a discontinuity in the transition between line orientations can be processed in parallel, i. e. that 'search' times increase by between 0.5 and 6 ms, on average, per additional element displayed, irrespective of the number of elements. But thresholds of orientation difference for the detection of the target increase linearly with the orientation gradient present in the display, and tend to increase more strongly for small gradients, indicating a special bonus for (near) collinearity. The averaged data follow a Weber-law type while this is not true for the individual observers' data. These results show that the visual system is indeed able to detect targets based on orientation contrast, rather than on absolute orientation [cf. Nothdurft (1985). Vision Research, 25, 551-560], but that the orientation gradient cannot be ignored.

Computer Graphics↗
PubMed1986

Molecular cloning and expression of neuroleukin, a neurotrophic factor for spinal and sensory neurons.

A novel 56,000-dalton growth factor found in mouse salivary gland was purified, molecularly cloned, and expressed in monkey COS cells. The protein is a neurotrophic factor and also, surprisingly, a lymphokine product of lectin-stimulated T cells. The factor was therefore named neuroleukin. Neuroleukin promotes the survival in culture of a subpopulation of embryonic spinal neurons that probably includes skeletal motor neurons. Neuroleukin also supports the survival of cultured sensory neurons that are insensitive to nerve growth factor, but has no effect on sympathetic or parasympathetic neurons. The amino acid sequence of neuroleukin is partly homologous to a highly conserved region of the external envelope protein of HTLV-III/LAV, the retrovirus that causes acquired immune deficiency syndrome.

Amino Acid Sequence↗
PubMed1986

Suppression of terminal axonal sprouting at the neuromuscular junction by monoclonal antibodies against a muscle-derived antigen of 56,000 daltons.

After the partial denervation or paralysis of a muscle, the remaining motor axon terminals may sprout fine, neuritic processes (terminal sprouts) which escape the endplate region of the neuromuscular junction. We previously identified a muscle-derived, protein antigen of 56,000 daltons (56 kD) which plays a necessary role in terminal sprouting. A panel of monoclonal antibodies have been produced against the 56-kD antigen, some of which also partially suppress motor axon terminal sprouting. These monoclonal antibodies define at least two different epitopes upon the surface of the antigen, one of which is necessary for it to effect its biological role in vivo.

Animals↗
PubMedDate not supplied

120 Hz oscillations in the flash visual evoked potential are strictly phase-locked and limited to the first 100 ms.

Flash stimulation elicits a visual evoked potential (VEP) as part of the electroencephalogram (EEG). This VEP is known to contain strong oscillatory activity around 120 Hz, which ceases 100 ms after the flash. It was unclear so far whether this time limit represents an averaging artifact due to loss of intertrial phase coherence or indicates a veridical cessation. Here we present results obtained from single-trial analysis of the EEG. These show that the oscillations exhibit virtually perfect phase locking and do in fact cease around 100 ms after the stimulus. Thus, the cessation of oscillatory activity in the VEP is not due to increasing intertrial phase jitter. Comparison with simultaneous retinal recordings exclude the possibility of direct crosstalk from the retina, but suggest that the oscillations are propagated from the retina to the cortex with a time lag of 48 ms.

Cerebral Cortex↗