Using Neuroimaging to Measure Mental Representations: Finding Color-OpponentNeurons in Visual Cortex

To date, most neuroimaging studies have tried to localize large regions in the brain that are responsible for specific behaviors or mental operations. Psychological theory, however, is more concerned with the nature of mental functions than with the locations of their neural substrates. This article reviews work that moves beyond functional anatomy to measure how color is represented by neurons in visual cortex. The general approach has three basic steps: First, the areas under investigation are localized in the brain. Second, responses of these areas are measured to sets of systematically varying stimuli, designed to uncover the nature of cortical representations. Third, the neuroimaging data are compared with behavioral data measured with the same stimuli. Results obtained using this approach support the hypothesis that primary visual cortex contains color-opponent neurons that support perception.     

Entorhinal but Not Hippocampal or Subicular Lesions Disrupt Latent Inhibition in Rats

Latent inhibition (LI) is the deficit of conditioning resulting from repeated nonreinforced preexposure to a conditioned stimulus before its pairing with an unconditioned stimulus. There are cumulative data showing that large lesions of the hippocampal formation disrupt LI. However, the effects of selective lesions of the different components of the hippocampal formation have never been directly addressed in the same study and conditioning paradigm. The first experiment of the present study aimed at investigating the effects of excitotoxic lesions of the hippocampus, subiculum, or entorhinal cortex on LI in an "off-baseline"-conditioned emotional response procedure. Hippocampus or subiculum lesions had no effect on either LI or conditioning. In contrast, entorhinal cortex lesions disrupted LI without modifying conditioning. In Experiment 2, locomotor activity in a novel environment was assessed in the same rats. Whereas lesions of hippocampus increased locomotor activity, lesions of the subiculum or the entorhinal cortex were devoid of effect. Although both LI and habituation to novel environmental cues are thought to involve interactions between the hippocampal formation and the mesolimbic pathway, these results indicate a functional dissociation between the hippocampus and the entorhinal cortex.     

Contribution of Ventrolateral Prefrontal Cortex to the Acquisition and Extinction of Conditioned Fear in Rats

The ventrolateral, agranular insular portion of prefrontal cortex (PFC) in rats is involved in visceral functions and has been shown to be involved in emotional processes. However, its contribution to aversive learning has not been well defined. Classical fear conditioning has been a powerful tool for illuminating some of the primary neural structures involved in aversive emotional learning. We measured both the acquisition and the extinction of conditioned fear following lesions of the ventrolateral PFC of rats. Lesions reduced fear reactivity to contextual stimuli associated with conditioning without affecting CS acquisition, and had no effect on response extinction. Ventrolateral PFC may normally be involved in the processing of contextual information while not being directly involved in extinction processes within the aversive domain.     

Interference and conflict monitoring in individuals with amnestic mild cognitive impairment: A structural study of the anterior cingulate cortex

Amnestic mild cognitive impairment (aMCI) is a clinical condition characterized by memory impairment in the absence of any other cognitive impairment and is commonly associated with high conversion to Alzheimer's disease. Recent evidence shows that executive functions and selective attention mechanisms could also be impaired in aMCI. In this study, we investigated performance differences (i.e., reaction times [RTs] and accuracy) between a group of aMCI participants and a group of age‐matched healthy individuals on the attentional network task (ANT) focusing on situations with increased interference. In particular, we assessed the relationship between interference and conflict effects and grey matter volumes (GMVs) of the anterior cingulate cortex (ACC)/pre‐supplementary motor area in the entire sample because of its crucial role in conflict monitoring. When compared with controls, aMCI participants were less accurate on the ANT, showing increased interference and conflict effects, but no differences in RTs. In addition, aMCI participants exhibited lower GMV in the ACC than controls. While better accuracy for interference and conflict effects was associated with an increase of GMV in the ACC for both groups, RTs from the interference effect were negatively correlated with GMV of the ACC only in aMCI participants. In other words, lower GMV values of the ACC were paralleled with significantly impaired performance in terms of interference resolution. In conclusion, our study suggests the presence of a selective impairment in interference and conflict monitoring in aMCI, which in turn is associated with decreased GMVs in the ACC.     

A social neuroscience perspective on adolescent risk-taking

This article proposes a framework for theory and research on risk-taking that is informed by developmental neuroscience. Two fundamental questions motivate this review. First, why does risk-taking increase between childhood and adolescence? Second, why does risk-taking decline between adolescence and adulthood? Risk-taking increases between childhood and adolescence as a result of changes around the time of puberty in the brain’s socio-emotional system leading to increased reward-seeking, especially in the presence of peers, fueled mainly by a dramatic remodeling of the brain’s dopaminergic system. Risk-taking declines between adolescence and adulthood because of changes in the brain’s cognitive control system—changes which improve individuals’ capacity for self-regulation. These changes occur across adolescence and young adulthood and are seen in structural and functional changes within the prefrontal cortex and its connections to other brain regions. The differing timetables of these changes make mid-adolescence a time of heightened vulnerability to risky and reckless behavior.     

The role of white matter hyperintensities and medial temporal lobe atrophy in age-related executive dysfunctioning

Various studies support an association between white matter hyperintensities (WMH) and deficits in executive function in nondemented ageing. Studies examining executive functions and WMH have generally adopted executive function as a phrase including various functions such as flexibility, inhibition, and working memory. However, these functions include distinctive cognitive processes and not all may be affected as a result of WMH. Furthermore, atrophy of the medial temporal lobe (MTA) is frequently observed in ageing. Nevertheless, in previous studies of nondemented ageing MTA was not considered when examining a relationship between white matter and executive function. The goal of the present study was to examine how WMH and MTA relate to a variety of executive functions, including flexibility, fluency, inhibition, planning, set shifting, and working memory. Strong correlations were observed between WMH and MTA and most of the executive functions. However, only MTA was related to flexibility and set shifting performance. Regression analysis furthermore showed that MTA was the strongest predictor of working memory, after which no further significant association with WMH was noted. Alternatively, both MTA and periventricular hyperintensities independently predicted inhibition performance. These findings emphasize the importance of MTA when examining age-related decline in executive functioning.     

Acetylcholine esterase activity and behavioral response in hypoxia induced neonatal rats: effect of glucose, oxygen and epinephrine supplementation

Brain damage due to an episode of hypoxia remains a major problem in infants causing deficit in motor and sensory function. Hypoxia leads to neuronal functional failure, cerebral palsy and neuro-developmental delay with characteristic biochemical and molecular alterations resulting in permanent or transitory neurological sequelae or even death. During neonatal hypoxia, traditional resuscitation practices include the routine administration of 100% oxygen, epinephrine and glucose. In the present study, we assessed the changes in the cholinergic system by measuring the acetylcholinesterase (AChE) activity and the behavioral responses shown by hypoxia induced neonatal rats and hypoxic rats supplemented with glucose, oxygen and epinephrine using elevated plus-maze and open-field test. The acetylcholine esterase enzyme activity showed a significant decrease in cerebral cortex, whereas it increased significantly in the muscle of experimental rats when compared to control. Hypoxic rats supplemented with glucose, glucose and oxygen showed a reversal to the control status. Behavioral studies were carried out in experimental rats with elevated plus-maze test and open-field test. Hypolocomotion and anxiogenic behavioral responses were observed in all experimental rats when compared to control, hypoxic rats supplemented with glucose, glucose and oxygen. Thus, our results suggest that brain damage due to hypoxia, oxygen and epinephrine supplementation in the neonatal rats cause acetylcholine-neuromuscular-defect leading to hypolocomotion and anxiogenic behavioral response. Glucose and glucose with oxygen supplementation to hypoxic neonates protect the brain damage for a better functional status in the later life.     

Freeze-Frame: a new infant inhibition task and its relation to frontal cortex tasks during infancy and early childhood

The current study investigated a new, easily administered, visual inhibition task for infants termed the Freeze-Frame task. In the new task, 9-month-olds were encouraged to inhibit looks to peripheral distractors. This was done by briefly freezing a central animated stimulus when infants looked to the distractors. Half of the trials presented an engaging central stimulus, and the other half presented a repetitive central stimulus. Three measures of inhibitory function were derived from the task and compared with performance on a set of frontal cortex tasks administered at 9 and 24 months of age. As expected, infants' ability to learn to selectively inhibit looks to the distractors at 9 months predicted performance at 24 months. However, performance differences in the two Freeze-Frame trial types early in the experiment also turned out to be an important predictor. The results are discussed in terms of the validity of the Freeze-Frame task as an early measure of different components of inhibitory function.     

Declarative Memory

ABSTRACT— Neuroimaging of declarative memory is not an endeavor divorced from psychology but, instead, is another path through which a more complete understanding of memory has emerged. Specifically, neuroimaging allows us to determine if differences between memory states emerge from quantitatively or qualitatively distinct underlying encoding operations. Further, it has allowed for greater specification of the putative control operations adopted when we make decisions about our memories. We describe some examples of insights provided by neuroimaging into the many and varied processes that support encoding and retrieval of declarative memory.