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Reports on placenta percreta in early pregnancy leading to a spontaneous rupture of the uterus are rare. We report a case of this potentially life-threatening complication in the 14th week of pregnancy in an otherwise healthy woman who underwent a manual extraction of the placenta during a previous delivery but who had no history of severe pathology that could have potentially resulted in uterine damage. The occurrence of severe abdominal pain and the presence of a large quantity of free fluid in the abdomen necessitated an emergency laparotomy, revealing a haemoperitoneum due to rupture of the uterus, which was followed by a hysterectomy. This case demonstrates that in patients with a history of placenta accreta and subsequent manual extraction of the placenta, a close investigation of the uterine wall and placentation should be performed in the first trimester in order to anticipate a placenta percreta.

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A recent study (Rossi et al. 2001) implied the absence of figure-ground based contextual modulation in macaque V1, in contrast to the study on which it was modelled (Zipser et al. 1996). We suggest that Rossi et al. may have underestimated the extent of modulation by considering only positive and not also negative modulation and that their data may have shown figure-ground based contextual modulation. We then suggest a paradigm to assess whether it reflects figure-ground segregation, boundaries, or both.

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To investigate the mechanism of transcranial magnetic stimulation (TMS), we compared the directional effects of two stimulators (Magstim 200 and Magstim Super Rapid). First, stimulating visual cortex and facial nerve with occipital mid-line TMS, we found that, for a particular coil orientation, these two stimulators affected a particular neural structure in opposite hemispheres and that, to affect a particular neural structure in a particular hemisphere, these two stimulators required opposite coil orientations. Second, stimulating a membrane-simulating circuit, we found that, for a particular coil orientation, these two stimulators resulted in a peak induced current of the same polarity but in a peak induced charge accumulation of opposite polarity. We suggest that the critical parameter in TMS is the amplitude of the induced charge accumulation rather than the amplitude of the induced current. Accordingly, TMS would be elicited just before the end of the first (Magstim 200) and second (Magstim Super Rapid) phase of the induced current rather than just after the start of the first phase of the induced current.

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We recently reported three periods when single-pulse transcranial magnetic stimulation (TMS) of the occipital pole impaired performance on a forced-choice visual letter-identification task. TMS-induced suppression during these periods is best explained by a blink-associated covering of the pupils and by a direct interference with letter-processing neural activity. We now report TMS-induced suppression at times that seem too late for the suppression to be explained by the first mechanism and too early for the suppression to be explained by the second mechanism. The most likely explanation is a blink-associated interference with letter-processing neural activity.

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We applied single-pulse transcranial magnetic stimulation (TMS) to the occipital pole of healthy subjects while they performed a forced-choice visual letter-identification task. We found three separate periods when TMS suppressed performance; the first period is best explained by TMS-induced blinking whereas the last two periods are best explained by TMS-induced disruption of letter-processing in the early visual cortex. Unexpectedly, we also found that TMS-induced suppression progressively disappeared during three weeks of repeated TMS experiments. However, it was only suppression during the last two periods that disappeared; suppression during the first period remained undiminished. When subjects were then presented with dimmer letters, suppression reappeared. The most likely explanation is a practice-induced increase in neuronal activity in the early visual cortex.

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To determine the timing of visual processing in the early visual cortex, we applied single pulse transcranial magnetic stimulation to the occipital pole of healthy subjects while they were engaged in a forced-choice visual letter-identification task. We found two separate periods of activity, the first ranging from 20 to 60 ms after the onset of the visual stimulus, and the second ranging from 100 to 140 ms after the onset of the visual stimulus. We suggest that these two periods reflect necessary activity in V1, before and after re-entry.

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To determine the timing of visual processing in the (circum)striate visual cortex, we examined the effect of single pulse transcranial magnetic stimulation over the occipital pole of healthy subjects who were engaged in a forced-choice visual letter identification task. Single letters, subtending a visual angle of 0.35 degrees, were foveally presented for 10 ms and were immediately followed by a mask. We investigated 30 different delays (d), defined as the time between the onset of the visual stimulus and the onset of the magnetic stimulus, from d = -100 ms to d = +190 ms, and 4 different midsagittal coil positions (x), defined as the distance between the lower edge of the coil and the upper edge of the inion, from x = 1 cm to x = 7 cm. Three out of four subjects showed three distinct delay intervals (dips) at which application of TMS resulted in an impairment of the task. The first dip was centred around d = -50 ms and occurred independently of the coil position; the second dip was centred around d = 0 ms and was elicitable only with the two lowest coil positions; the third dip was centred around d = 100 ms and was also elicitable only with the lower coil positions. In the fourth subject, only the first and the third dip were found. We conclude that there are two distinct periods when the activity in the (circum)striate visual cortex is necessary for the identification of visually presented letters.

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The dielectric properties of tissues have been extracted from the literature of the past five decades and presented in a graphical format. The purpose is to assess the current state of knowledge, expose the gaps there are and provide a basis for the evaluation and analysis of corresponding data from an on-going measurement programme.

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