Neurally constrained modeling of perceptual decision making

Stochastic accumulator models account for response time in perceptual decision-making tasks by assuming that perceptual evidence accumulates to a threshold. The present investigation mapped the firing rate of frontal eye field (FEF) visual neurons onto perceptual evidence and the firing rate of FEF movement neurons onto evidence accumulation to test alternative models of how evidence is combined in the accumulation process. The models were evaluated on their ability to predict both response time distributions and movement neuron activity observed in monkeys performing a visual search task. Models that assume gating of perceptual evidence to the accumulating units provide the best account of both behavioral and neural data. These results identify discrete stages of processing with anatomically distinct neural populations and rule out several alternative architectures. The results also illustrate the use of neurophysiological data as a model selection tool and establish a novel framework to bridge computational and neural levels of explanation.

Neural correlates of correct and errant attentional selection revealed through N2pc and frontal eye field activity

The goal of this study was to obtain a better understanding of the physiological basis of errors of visual search. Previous research has shown that search errors occur when visual neurons in the frontal eye field (FEF) treat distractors as if they were targets. We replicated this finding during an inefficient form search and extended it by measuring simultaneously a macaque homologue of an event-related potential indexing the allocation of covert attention known as the m-N2pc. Based on recent work, we expected errors of selection in FEF to propagate to areas of extrastriate cortex responsible for allocating attention and implicated in the generation of the m-N2pc. Consistent with this prediction, we discovered that when FEF neurons selected a distractor instead of the search target, the m-N2pc shifted in the same, incorrect direction prior to the erroneous saccade. This suggests that such errors are due to a systematic misorienting of attention from the initial stages of visual processing. Our analyses also revealed distinct neural correlates of false alarms and guesses. These results demonstrate that errant gaze shifts during visual search arise from errant attentional processing.

On the origin of event-related potentials indexing covert attentional selection during visual search

Despite nearly a century of electrophysiological studies recording extracranially from humans and intracranially from monkeys, the neural generators of nearly all human event-related potentials (ERPs) have not been definitively localized. We recorded an attention-related ERP component, known as the N2pc, simultaneously with intracranial spikes and local field potentials (LFPs) in macaques to test the hypothesis that an attentional-control structure, the frontal eye field (FEF), contributed to the generation of the macaque homologue of the N2pc (m-N2pc). While macaques performed a difficult visual search task, the search target was selected earliest by spikes from single FEF neurons, later by FEF LFPs, and latest by the m-N2pc. This neurochronometric comparison provides an empirical bridge connecting macaque and human experiments and a step toward localizing the neural generator of this important attention-related ERP component.

Population encoding by circadian clock neurons organizes circadian behavior

Mammalian circadian rhythms are orchestrated by the suprachiasmatic nuclei (SCN) of the hypothalamus. The SCN are composed of circadian clock neurons, but the mechanisms by which these populations of neuronal oscillators encode rhythmic behavior are incompletely understood. We have used ex vivo real-time gene expression imaging of the neural correlates of circadian behavior, combined with genetic disruption of vasoactive intestinal polypeptide, a key SCN signaling molecule, to examine the neural basis of circadian organization in the SCN. We show that the coherence and timing of clock neuron rhythms are correlated with the coherence and timing of behavioral rhythms within individual mice and that the degree of disruption of SCN neuronal organization correlates with the degree of behavioral disruption within individuals. Our results suggest that the SCN encode circadian phase as a temporal population vector of its constituent neurons; such that as the neuronal population becomes desynchronized, phase information becomes ambiguous.

Neural basis of the set-size effect in frontal eye field: timing of attention during visual search

Visual search for a target object among distractors often takes longer when more distractors are present. To understand the neural basis of this capacity limitation, we recorded activity from visually responsive neurons in the frontal eye field (FEF) of macaque monkeys searching for a target among distractors defined by form (randomly oriented T or L). To test the hypothesis that the delay of response time with increasing number of distractors originates in the delay of attention allocation by FEF neurons, we manipulated the number of distractors presented with the search target. When monkeys were presented with more distractors, visual target selection was delayed and neuronal activity was reduced in proportion to longer response time. These findings indicate that the time taken by FEF neurons to select the target contributes to the variation in visual search efficiency.

Biophysical support for functionally distinct cell types in the frontal eye field

Numerous studies have described different functional cell types in the frontal eye field (FEF), but the reliability of the distinction between these types has been uncertain. Studies in other brain areas have described specific differences in the width of action potentials recorded from different cell types. To substantiate the functionally defined cell types encountered in FEF, we measured the width of spikes of visual, movement, and visuomovement types of FEF neurons in macaque monkeys. We show that visuomovement neurons had the thinnest spikes, consistent with a role in local processing. Movement neurons had the widest spikes, consistent with their role in sending eye movement commands to subcortical structures such as the superior colliculus. Visual neurons had wider spikes than visuomovement neurons, consistent with their role in receiving projections from occipital and parietal cortex. These results show how structure and function of FEF can be linked to guide inferences about neuronal architecture.

Difficulty of visual search modulates neuronal interactions and response variability in the frontal eye field

The frontal eye field (FEF) is involved in selecting visual targets for eye movements. To understand how populations of FEF neurons interact during target selection, we recorded activity from multiple neurons simultaneously while macaques performed two versions of a visual search task. We used a multivariate analysis in a point process statistical framework to estimate the instantaneous firing rate and compare interactions among neurons between tasks. We found that FEF neurons were engaged in more interactions during easier visual search tasks compared with harder search tasks. In particular, eye movement-related neurons were involved in more interactions than visual-related neurons. In addition, our analysis revealed a decrease in the variability of spiking activity in the FEF beginning approximately 100 ms before saccade onset. The minimum in response variability occurred approximately 20 ms earlier for the easier search task compared with the harder one. This difference is positively correlated with the difference in saccade reaction times for the two tasks. These findings show that a multivariate analysis can provide a measure of neuronal interactions and characterize the spiking activity of FEF neurons in the context of a population of neurons.

Rothmund-Thomson syndrome and osteosarcoma

The Rothmund-Thomson syndrome (RTS), also called poikiloderma congenitale is a rare autosomal recessive disease first described in 1868. This syndrome includes most frequently seen skin lesions (atrophy, telangiectases, pigmentation), cataracts and bone defects (dysostosis, dysplasia). Some authors describe an association with malignancy. We report three cases of Rothmund-Thomson syndrome associated with osteosarcoma. After cutaneous epithelioma, osteosarcoma is the most frequent malignancy. Thus, patients with RTS need a careful survey. The treatment did not differ from sporadic osteosarcoma. Chemosensitivity and toxicity are also not different.

Probable disseminated cerebral aspergillosis: recovery with medical treatment

Cerebral aspergillosis has a very poor prognosis. When this complication occurs in the immunocompromised host, evolution is virtually fatal in all cases despite surgical and medical treatment. We describe in this report the case of a child with acute lymphoblastic leukaemia who developed pulmonary aspergillosis, and subsequent cerebral dissemination during therapeutic induction. Due to multifocal cerebral lesions, surgery was impossible. The patient was administered long term treatment including amphotericin B, flucytosine and itraconazole for 9 months, during which time a neutropenic period occurred with reactivation of cerebral mycotic lesions, in spite of modification of antileukaemic therapy. Seven years later, he nevertheless remains in complete remission without any neurological sequelae. Thus cerebral aspergillosis requires early diagnosis and can be treated using a strong combination of antimycotic drugs (amphotericin B, flucytosine and itraconazole) on a long term basis, even when aspergillomas cannot be removed surgically. Antileukaemic therapy must be concomitantly adapted to avoid or limit neutropenia.

[Precocious puberty revealing Bourneville tuberous sclerosis]

BACKGROUND

Benign tumors are seen in tuberous sclerosis. They are found in many organs, and the precocious puberty due to hypothalamic hamartoma and tuberous sclerosis has been reported. However, precocious puberty exceptionally reveals the tuberous sclerosis.

CASE REPORT

A 2 month-old boy was admitted because of the fortuitous discovery of polycystic renal disease. Precocious puberty developed at 13 months with enlargement of the penis and testes, appearance of pubic hair, acne and deepening of the voice. Linear growth was recently accelerated and the bone maturation was advanced. Plasma testosterone was elevated (460 ng/100 ml) and LH-RH injection induced rapid rises in plasma LH (2.6 to 28 mUl/ml) and FSH (2 to 8 mUl/ml). Brain imaging techniques (CT scan and NMR) showed a hypothalamic hamartoma and periventricular calcified lesions. Examination with the Wood lamp identified two white leaf macules in the dorsal area. Administration of an analogue of LH-RH effectively reduced the manifestations of precocious puberty.

CONCLUSION

Tuberous sclerosis is exceptionally revealed by precocious puberty. The association of polycystic disease and precocious puberty has never before been reported in tuberous sclerosis.

Anatomical study of five prenataly diagnosed sternopagus twins

Among conjoined twins (1 out 50000 births), thoracopagus occurs most frequently and is generally lethal. Our anatomical study of five sets of sternopagus twins (3 female, 2 male) was performed to determine the ability of prenatal sonography to detect these anomalies. Autopsy in four cases revealed identical malformations: common sternum, single malformed heart, joined hepatic parenchyma, and a common small bowel leading to a cystic dilatation situated on the ileal segment at the end of the superior mesenteric artery. The diagnosis of conjoined twins was made in all cases by prenatal sonography at the mean time of 24.6 gestation weeks (range 19-34). The malformations detected by prenatal sonography were a single cardiac mass (all cases), joined hepatic parenchymas (3 cases), and an ileal cystic dilatation (1 case). Pregnancy was terminated in four cases. In one case cesarean delivery was performed, and the infants died 48 hours later. Prenatal sonography currently seems to be the best examination for diagnosis of sternopagus twins and the detection of lethal malformations thus allowing interruption of pregnancy.

MRI evaluation of the levator ani muscle: anatomic correlations and practical applications

A comparative study of serial anatomic sections in the transverse, frontal and sagittal planes with corresponding MRI sections of the pelvis allowed the authors to define the most suitable sectional planes and MRI modes for a morphologic study of the levator ani muscle. This study shows the value of MRI examination in the assessment of anorectal malformations.

[Torsion of normal adnexa in children]

Seven cases of torsion of normal uterine adnexa are reported in children aged 4 to 15 years. In one case diagnosis was made by ultrasonography, allowing conservative treatment under coelioscopy. In the 6 other cases the necrosis of the ovary required its excision. The torsion concerned the ovary and uterine tube in 6 cases and the uterine tube alone in one. In 2 cases, the apparently healthy contralateral ovary was enlarged. From this series, the authors review the clinical and ultrasonographic features of the torsion of normal uterine adnexa. Ultrasonography should be performed in emergency as the conservation of the ovary depends on the precocity of diagnosis and treatment.

[Lateral tracheal indentation or compression by the brachiocephalic arterial trunk in children]

Three cases of compression of the right wall of the trachea by buckling of the innominate artery in childhood are described. A coarctation of the thoracic aorta is associated in two cases, and a left cervical aortic arch in the third one. In one case, a severe tracheomalacia occurs following the surgical repair of the associated coarctation. This lateral indentation of the trachea is suggestive of right aortic arch but the absence of posterior oesophageal indentation excludes the diagnosis. Angiography is helpful and echography is unable to demonstrate the vascular origin of the tracheal compression. The authors analyse the correct diagnostic approach, emphasize the risk of tracheomalacia and the high rate of associated cardio-vascular malformations.

[Prenatal diagnosis of pulmonary hypoplasia camptodactyly syndrome. Hypothesis concerning the origin of hydramnios]

Camptodactyly and pulmonary hypoplasia syndrome was described for the first time in 1974. Today 15 cases have been found. None were subject to a prenatal diagnosis as any ultrasonography. The case we observe is a 27 years old woman, third gestation, showing a polyhydramnios at 25 weeks of gestation. The ultrasonographic examination showed deformation with a rounded abdomen, a narrow thoracic frame slightly concave, no gastric picture and hands in constant flexion. After elimination of the V.A.T.E.R.' syndrome the camptodactyly's syndrome with pulmonary hypoplasia was proposed. Because of the lethal character of this syndrome, the abortion was realised. The photos of the fetus were the same as the ultrasonographic pictures during the prenatal diagnosis. The absence of intrinsic (paralysis) or extrinsic (compression) movements of the fetus is very important in the genesis of "deformations". The severity of the deformities depends on the importance of akinesia.