Neuronal correlates of tactile working memory in rat barrel cortex and prefrontal cortex

The neuronal mechanisms of parametric working memory \u2013 the short-term storage of graded stimuli to guide behavior \u2013 are not fully elucidated. We have designed a working memory task where rats compare two sequential vibrations, S1 and S2, delivered to their whiskers (Fassihi et al, 2014). Vibrations are a series of velocities sampled from a zero-mean normal distribution. Rats must judge which stimulus had greater velocity standard deviation, \u3c3 (e.g. \u3c31 > \u3c32 turn left, \u3c31 < \u3c32 turn right). A critical operation in this task is to hold S1 information in working memory for subsequent comparison. In an earlier work we uncovered this cognitive capacity in rats (Fassihi et al, 2014), an ability previously ascribed only to primates. Where in the brain is such a memory kept and what is the nature of its representation? To address these questions, we performed simultaneous multi-electrode recordings from barrel cortex \u2013 the entryway of whisker sensory information into neocortex \u2013 and prelimbic area of medial prefrontal cortex (mPFC) which is involved in higher order cognitive functioning in rodents. During the presentation of S1 and S2, a majority of neurons in barrel cortex encoded the ongoing stimulus by monotonically modulating their firing rate as a function of \u3c3; i.e. 42% increased and 11% decreased their firing rate for progressively larger \u3c3 values. During the 2 second delay interval between the two stimuli, neuronal populations in barrel cortex kept a graded representation of S1 in their firing rate; 30% at early delay and 15% at the end. In mPFC, neurons expressed divers coding characteristics yet more than one-fourth of them varied their discharge rate according to the ongoing stimulus. Interestingly, a similar proportion carried the stimulus signal up to early parts of delay period. A smaller but considerable proportion (10%) kept the memory until the end of delay interval. We implemented novel information theoretic measures to quantify the stimulus and decision signals in neuronal responses in different stages of the task. By these measures, a decision signal was present in barrel cortex neurons during the S2 period and during the post stimulus delay, when the animal needed to postpone its action. Medial PFC units also represented animal choice, but later in the trial in comparison to barrel cortex. Decision signals started to build up in this area after the termination of S2. We implemented a regularized linear discriminant algorithm (RDA) to decode stimulus and decision signals in the population activity of barrel cortex and mPFC neurons. The RDA outperformed individual clusters and the standard linear discriminant analysis (LDA). The stimulus and animal\u2019s decision could be extracted from population activity simply by linearly weighting the responses of neuronal clusters. The population signal was present even in epochs of trial where no single cluster was informative. We predicted that coherent oscillations between brain areas might optimize the flow of information within the networks engaged by this task. Therefore, we quantified the phase synchronization of local field potentials in barrel cortex and mPFC. The two signals were coherent at theta range during S1 and S2 and, interestingly, prior to S1. We interpret the pre-stimulus coherence as reflecting top-down preparatory and expectation mechanisms. We showed, for the first time to our knowledge, the neuronal correlates of parametric working memory in rodents. The existence of both positive and negative codes in barrel cortex, besides the representation of stimulus memory and decision signals suggests that multiple functions might be folded into single modules. The mPFC also appears to be part of parametric working memory and decision making network in rats

A Low-Complexity Near-Optimal Detector for Multispan Zero-Dispersion Fiber-Optic Channels

We design a novel receiver based on the theoretical finding that the linear phase noise is uncorrelated with the nonlinear phase noise. The implementation of the proposed receiver is straightforward and it performs almost equally to the optimal detector at a much lower complexity

Data on heavy metal levels (Cd, Co, and Cu) in wheat grains cultured in Dashtestan County, Iran.

Due to importance of wheat as the most popular food, in this data article, we determined the accumulation of heavy metal levels including Cd, Co, and Cu in wheat grains in Dashtestan county, Iran. The concentration levels of heavy metals in wheat grains cultured were determined by Flame Atomic Absorption Spectrometry (FAAS)

Niphargus sarii sp. n., a new subterranean niphargid (Crustacea: Amphipoda) from Iran based on molecular and morphological characters

Niphargus sarii sp. n. was collected from Jo-Khanem Spring in Ilam Province. This species hypothesis is based on the analysis of morphological characters and 28S ribosomal DNA sequences. In this paper, we describe the morphological traits of this new species. Then, its taxonomic status within the genus is discussed in comparison to the 15 known Iranian species. Results revealed that N. sarii sp. n. is phylogenetically close to N. sohrevardensis. This species is easily distinguished from other Iranian species by some characters, in particular the equal length of rami in uropod I, lack of lateral robust setae on telson and the situation of dactylus to posterior margin of propodus in gnathopod II

Maternal Separation and the Risk of Drug Abuse in Later Life

Maternal separation (MS) is defined as the termination of the continuity of mother-child relationship after the relationship is established. Although MS and maternal deprivation are different in terms of their definitions, these two terms are usually used interchangeably. This review aims to investigate the effect of MS on drug intake in adulthood. It has been proved that animal models are helpful in evaluating the effects of MS on drug intake risk in adulthood. There are relatively acceptable studies in this field on some drugs such as morphine, ethanol, and cocaine. However, very few animal studies, or even no animal study, have been conducted on some other drugs. The majority of these studies have considered MS as a risk factor for drug intake in adulthood. Different mechanisms are proposed for this phenomenon. Brain reward pathways are one of the main exploratory pathways of this process. Despite the importance of the issue, no human study with a specific concentration on investigating the relationship between MS and drug abuse in later life was found. Causal studies are warranted on humans to investigate the effect of MS on drug intake in later life