Detection of Gabor patterns of different sizes, shapes, phases and eccentricities

Contrast thresholds of vertical Gabor patterns were measured as a function of their eccentricity, size, shape, and phase using a 2AFC method. The patterns were 4 c/deg and they were presented for 90 or 240 ms. Log thresholds increase linearly with eccentricity at a mean rate of 0.47 dB/wavelength. For patterns centered on the fovea, thresholds decrease as the area of the pattern increases over the entire standard deviation range of 12 wavelengths. The TvA functions are concave up on log-log coordinates. For small patterns there is an interaction between shape and size that depends on phase. Threshold contrast energy is a U-shaped function of area with a minimum in the vicinity of 0.4 wavelength indicating detection by small receptive fields. Observers can discriminate among patterns of different sizes when the patterns are at threshold indicating that more than one mechanism is involved. The results are accounted for by a model in which patterns excite an array of slightly elongated receptive fields that are identical except that their sensitivity decreases exponentially with eccentricity. Excitation is raised to a power and then summed linearly across receptive fields to determine the threshold. The results are equally well described by an internal-noise-limited model. The TvA functions are insufficient to separately estimate the noise and the exponent of the power function. However, an experiment that shows that mixing sizes within the trial sequence has no effect on thresholds, suggests that the limiting noise does not increase with the number of mechanisms monitored.     

Improved preoperative planning for directed parathyroidectomy with 4-dimensional computed tomography

BACKGROUND: Four-dimensional computed tomography (4D-CT) provides both functional and highly detailed anatomic information about parathyroid tumors. The purpose of this study was to compare 4D-CT with sestamibi imaging and ultrasonography as methods for the accurate preoperative localization of hyperfunctioning parathyroid glands before parathyroidectomy. METHODS: A study of 75 patients with primary hyperparathyroidism was performed at a tertiary-care institution. Sestamibi imaging, ultrasonography, and 4D-CT were performed on each patient preoperatively. Results of the imaging studies were compared with operative findings, pathologic data, and biochemical measurements to assess the sensitivity and specificity of each of the imaging modalities. RESULTS: 4D-CT demonstrated improved sensitivity (88%) over sestamibi imaging (65%) and ultrasonography (57%), when the imaging studies were used to localize (lateralize) hyperfunctioning parathyroid glands to 1 side of the neck. Moreover, when used to localize parathyroid tumors to the correct quadrant of the neck (ie, right inferior, right superior, left inferior, or left superior), the sensitivity of 4D-CT (70%) was significantly higher than sestamibi imaging (33%) and ultrasonography (29%). CONCLUSION: 4D-CT provides significantly greater sensitivity than sestamibi imaging and ultrasonography for precise (quadrant) localization of hyperfunctioning parathyroid glands. This allows improved preoperative planning, particularly for the case of reoperation. In addition to the data that are provided, we present a novel classification scheme for use in parathyroid localization.     

Surgical treatment of hyperparathyroidism in patients with multiple endocrine neoplasia type 1

HYPOTHESIS: Three-gland parathyroidectomy with trans-cervical thymectomy and cryopreservation is the preferred initial surgical approach for hyperparathyroidism (HPT) in patients with multiple endocrine neoplasia type 1. DESIGN: Retrospective cohort study. SETTING: Tertiary referral center. PATIENTS: Thirty-seven patients with multiple endocrine neoplasia type 1 who underwent 1 or more surgical procedures for HPT from January 1, 1973 to April 30, 2004. RESULTS: At initial parathyroid surgery, 16 (43%) of 37 patients had fewer than 3 parathyroid glands resected (group 1); 16 (43%) had at least 3 but fewer than 4 glands (group 2), and 5 (14%), 4 or more glands (group 3). Follow-up of at least 6 months after initial surgery was complete for 31 (84%) of 37 patients. CONCLUSIONS: Recurrent HPT in patients with multiple endocrine neoplasia type 1 is frequent if fewer than 3 glands are removed at initial parathyroidectomy. Optimal surgical intervention must balance the risk of recurrent hypercalcemia with the morbidity of permanent hypoparathyroidism. Three-gland parathyroidectomy, transcervical thymectomy, and parathyroid cryopreservation constitute our preferred initial surgical procedure.     

Activity sampling in the assessment of patients with total joint arthroplasty

Quantitative assessment of patient activity is important in evaluating the outcomes of joint prostheses, and such methods are gaining popularity. The single greatest impediment to quantitative activity assessment is patient compliance. How many days of sampling are necessary to provide reliable and accurate estimates of walking activity? The current study analyzes how well sampling for 4 consecutive days of activity compares to assessing activity for 7 or more days with the same pedometer in 131 patients with either a total hip or total knee prosthesis. The mean steps per day obtained throughout the full-length sampling (7-123 days) was strongly correlated to the one obtained from the random consecutive 4-day sample (r² = 0.94, P < .001) with only 5 outliers. The 4-day activity assessment gave an underestimation of 4.7% (P = .5). The number of outliers increased with fewer days of sampling. Monitoring activity for 4 consecutive days yields a quantitative assessment that is within 5% of a sampling of 7 or more days.     

Proenkephalin A gene products activate a new family of sensory neuron--specific GPCRs

Several peptide fragments are produced by proteolytic cleavage of the opioid peptide precursor proenkephalin A, and among these are a number of enkephalin fragments, in particular bovine adrenal medulla peptide 22 (BAM22). These peptide products have been implicated in diverse biological functions, including analgesia. We have cloned a newly identified family of 'orphan' G protein--coupled receptors (GPCRs) and demonstrate that BAM22 and a number of its fragments bind to and activate these receptors with nanomolar affinities. This family of GPCRs is uniquely localized in the human and rat small sensory neuron, and we called this family the sensory neuron--specific G protein--coupled receptors (SNSRs). Receptors of the SNSR family are distinct from the traditional opioid receptors in their insensitivity to the classical opioid antagonist naloxone and poor activation by opioid ligands. The unique localization of SNSRs and their activation by proenkephalin A peptide fragments indicate a possible function for SNSRs in sensory neuron regulation and in the modulation of nociception.