A dissociation between human neural systems that participate in the encoding and later recognition of new memories for faces was demonstrated by measuring memory task-related changes in regional cerebral blood flow with positron emission tomography. There was almost no overlap between the brain structures associated with these memory functions. A region in the right hippocampus and adjacent cortex was activated during memory encoding but not during recognition. The most striking finding in neocortex was the lateralization of prefrontal participation. Encoding activated left prefrontal cortex, whereas recognition activated right prefrontal cortex. These results indicate that the hip-pocampus and adjacent cortex participate in memory function primarily at the time of new memory encoding. Moreover, face recognition is not mediated simply by recapitulation of operations performed at the time of encoding but, rather, involves anatomically dissociable operations. In humans and nonhuman primates, damage to the hippocam-pus and adjacent cortex produces a profound anterograde amnesic syndrome that impairs the ability to form and store new explicit memories (1-5). Although recall for previously stored information can remain largely intact (1, 4, 6), the retrieval of recently formed memories may be impaired (3). Thus, for a limited time after initial storage, access to memories does depend on the integrity of the medial temporal structures, suggesting that these structures may actively participate not only in memory storage but also in the retrieval of recently stored memories. Despite this clear evidence of memory impairment after medial temporal lesions, functional brain imaging studies of human memory have been mostly unsuccessful in demonstrating the participation of the hippocampus and adjacent cortex in either the encoding or the retrieval of new long-term memories (7-12). These same studies, however, consistently demonstrate that the frontal lobes participate in episodic memory encoding and retrieval, although studies of the effects of frontal lobe lesions suggest these areas do not play a critical role in episodic memory processing (13-18). Most previous functional brain imaging studies of memory have used verbal materials and have demonstrated a functional dissociation between left and right prefrontal areas. Whereas left prefron-tal areas are activated during episodic verbal memory encoding , right prefrontal areas are activated during retrieval. Although some studies suggest that right prefrontal areas might also be involved in the retrieval of nonverbal long-term memories, no studies of nonverbal memory encoding have been reported. To clarify the roles played by these brain structures in episodic memory, we investigated memory for a different type The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. of information-namely faces-using an experimental design t...

Although melatonin deficiency may cause scoliosis in the chicken, this study suggests that it is not a mechanism in the pathogenesis of adolescent idiopathic scoliosis in humans.

We describe a rapid, sensitive method for the routine simultaneous determination of nicotine and cotinine in 1 mL of plasma. Extraction in 10-mL screw-capped Teflon tubes with methylene chloride after deproteinization with trichloroacetic acid eliminated emulsion formation. The extract, after evaporation and reconstitution in 30 microL of mobile phase, is injected into a reversed-phase C-18 ion-pair column of an isocratic high-performance liquid-chromatographic unit. Absorbance is monitored at 256 nm. The mobile phase is a citrate-phosphate (30 mmol each per liter) buffer mixture containing 50 mL of acetonitrile and 1 mmol of sodium heptanesulfonate per liter. 2-Phenylimidazole is the internal standard. The detection limit is 1 microgram/L for nicotine and 3 micrograms/L for cotinine. The standard curve is linear from 0 to 700 micrograms/L for both compounds. The average CV for nicotine in the concentration range 0-100 micrograms/L is 6.5%, and that for cotinine in the concentration range 50-700 micrograms/L is 4%.

A reversed-phase liquid chromatographic method for the separation of 26 phenylthiocarbamyl derivatives of amino acids in human plasma in ca. 35 min. is described. The method used a C,, column (150 x 4.6 mm I.D., 3 pm) thermostatted at 41°C and a simple multistep linear gradient of two solvents. Solvent A was 0.05 A4 sodium acetate (PH 5.1)-acetonitrile (98:2, v/v), and solvent B was water-acetonitrile (40:60, v/v). A simple and successful approach to the optimization of the conditions for the separation of the 26 amino acid derivatives was realized. In the initial phase of development, the composition of the gradient, its timings, the column temperature, the flow-rate and the mobile phase compositions were optimized. At the end the influence of pH was studied, and this approach led to a clear resolution of the 26 amino acids. The method was validated by accuracy, precision, and recovery studies, by analyzing patient samples, and by comparing the quality control sample results with the classical ion-exchange method.

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