2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), which is produced during cooking and is mutagenic to bacteria and cultured mammalian cells, was found to induce high incidences of colon and mammary carcinomas in F344 rats when administered at a concentration of 400 p.p.m. in the diet for 52 weeks. Since PhIP is the most abundant of the mutagenic heterocyclic amines in cooked meat and fish, the compound might be related to malignancies of the colon and breast in humans.

Ratcliff R, Hasegawa YT, Hasegawa RP, Smith PL, Segraves MA. Dual diffusion model for single-cell recording data from the superior colliculus in a brightness-discrimination task. J Neurophysiol 97: 1756Neurophysiol 97: -1774Neurophysiol 97: , 2007. First published November 22, 2006; doi:10.1152/jn.00393.2006. Monkeys made saccades to one of two peripheral targets based on the brightness of a central stimulus. Task difficulty was manipulated by varying the ratio of stimulus black-and-white pixels. Correct response probability for two monkeys varied directly with difficulty. Deep layer SC neurons exhibited robust presaccadic activity the magnitude of which was unaffected by task difficulty when the stimulus specified a saccade toward a target within the neuron's response field. Activity after stimuli specifying saccades to targets outside the response field was affected by task difficulty, increasing as the task became more difficult. A quantitative model derived from studies of human decision-making was fit to the behavioral data. The model assumes that information from the stimulus drives two independent diffusion processes. Simulated paths from the model were compared with neuron activity, assuming that firing rate is linearly related to position in the accumulation process. The firing rate data show delayed availability of discriminative information for fast, intermediate, and slow decisions when activity is aligned on the stimulus and very small differences in discriminative information when aligned on the saccade. The model produces exactly these patterns of results. The accumulation process is highly variable, allowing the process both to make errors, as is the case for the behavioral performance, and also to account for the firing rate results. Thus the dual diffusion model provides a quantitative account for both the behavior in a simple decision-making task as well as the patterns of activity in competing populations of neurons. I N T R O D U C T I O NResearch in neural decision making is at the point of identifying the mechanisms that implement simple decisions (Glimcher and Sparks 1992;Gold and Shadlen 2000;Hanes and Schall 1996; Newsome 1999, 2001;Kim and Shadlen 1999;Krauzlis and Dill 2002;McPeek and Keller 2002;Ratcliff et al. 2003a;Roitman and Shadlen 2002;Romo et al. 2002;Sparks 1999). In parallel to this work, psychology has produced a set of models that describe simple rapid two-choice decision making Townsend 1992, 1993;Diederich 1997;LaBerge 1994;Laming 1968;Link 1975;Link and Heath 1975; Pike 1966Pike , 1973Ratcliff 1978Ratcliff , 1981Ratcliff , 1988 Rouder 1998, 2000;Ratcliff and Smith 2004;Ratcliff et al. 1999;Roe et al. 2001;Smith 1995;Smith and Ratcliff 2004;Smith and Van Zandt 2000;Stone 1960;Townsend and Ashby 1983). We present a diffusion model that explicitly relates these two domains in the context of a single experiment. The model is applied to simple twochoice decisions and accounts for both behavioral data, namely, accuracy and correct and error response time (RT) distributi...

Gastric and intestinal phenotypic expression in 223 surgically obtained primary gastric cancers and their histogenetic relationship to intestinal metaplasia in the surrounding gastric mucosa were studied by mucin histochemistry and pepsinogen (Pg) immunohistochemistry. Histochemical differentiation of mucins (paradoxical concanavalin A, the galactose oxidase‐Schiff sequence and sialidase galactose oxidase Schiff) and immunohisto chemical staining of Pgs I and II, allowed differentiation of gastric cancer cells from different histological categories into gastric elements including mucous neck cells, pyloric gland cells and surface mucous cells or intestinal elements including goblet cell and intestinal absorptive cell types. Of 122 papillary and tubular adenocarcinomas, 33 (27.1%) consisted mainly of gastric type cells and 42 (34.4%) predominantly of intestinal type cells. The remainder (38.5%) consisted of mixtures of gastric‐ and intestinal‐type cells. Of 101 poorly differentiated adenocarcinomas, signet ring cell carcinomas and mucinous adenocarcinomas, 59 (58.4%) consisted mainly of gastric‐type cells and 20 (19.8%) mainly of intestinal‐type cells. Seven out of 35 papillary and tubular adenocarcinomas consisting mainly of gastric type cancer cells were surrounded by mucosa with intestinal metaplasia. Conversely, 10 out of 40 papillary and tubular adenocarcinomas consisting mainly of intestinal‐type cancer cells were observed in non metaplastic gastric mucosa. Thus no relationship as regards intestinal phenotypic expression was found between gastric cancers and surrounding gastric mucosa.

The prefrontal cortex has been implicated in the suppression of unwanted behavior, based upon observations of humans and monkeys with prefrontal lesions. Despite this, there has been little direct neurophysiological evidence for a mechanism that suppresses specific behavior. In this study, we used an oculomotor delayed match/nonmatch-to-sample task in which monkeys had to remember a stimulus location either as a marker of where to look or as a marker of where not to look. We found a group of neurons in both the frontal eye field and the caudal prefrontal cortex that carried signals selective for the forbidden stimulus. The activity of these "don't look" neurons correlated with the monkeys' success or failure on the task. These results demonstrate a frontal signal that is related to the active suppression of one action while the subject performs another.