A Possible Role for Cholinergic Neurons of the Basal Forebrain and Pontomesencephalon in Consciousness

Excitation at widely dispersed loci in the cerebral cortex may represent a neural correlate of consciousness. Accordingly, each unique combination of excited neurons would determine the content of a conscious moment. This conceptualization would be strengthened if we could identify what orchestrates the various combinations of excited neurons. In the present paper, cholinergic afferents to the cerebral cortex are hypothesized to enhance activity at specific cortical circuits and determine the content of a conscious moment by activating certain combinations of postsynaptic sites in select cortical modules. It is proposed that these selections are enabled by learning-related restructuring that simultaneously adjusts the cytoskeletal matrix at specific constellations of postsynaptic sites giving all a similar geometry. The underlying mechanism of conscious awareness hypothetically involves cholinergic mediation of linkages between microtubules and microtubule-associated protein-2 (MAP-2). The first reason for proposing this mechanism is that previous studies indicate cognitive-related changes in MAP-2 occur in cholinoceptive cells within discrete cortical modules. These cortical modules are found throughout the cerebral cortex, measure 1–2 mm², and contain approximately 10³–10⁴cholinoceptive cells that are enriched with MAP-2. The subsectors of the hippocampus may function similarly to cortical modules. The second reason for proposing the current mechanism is that the MAP-2 rich cells throughout the cerebral cortex correspond almost exactly with the cortical cells containing muscarinic receptors. Many of these cholinoceptive, MAP-2 rich cells are large pyramidal cell types, but some are also small pyramidal cells and nonpyramidal types. The third reason for proposing the current mechanism is that cholinergic afferents are module-specific; cholinergic axons terminate wholly within individual cortical modules. The cholinergic afferents may be unique in this regard. Finally, the tapering apical dendrites of pyramidal cells are proposed as primary sites for cholinergic mediation of linkages between MAP-2 and microtubules because especially high amounts of MAP-2 are found here. Also, the possibility is raised that muscarinic actions on MAP-2 could modulate microtubular coherence and self-collapse, phenomena that have been suggested to underlie consciousness.     

Amygdala and Periaqueductal Gray Lesions Only Partially Attenuate Unconditional Defensive Responses in Rats Exposed to a Cat

Defensive responses to a cat were observed in rats given excitotoxic lesions of the central nucleus of the amygdala (ACe), dorsolateral periaqueductal gray (dlPAG), ventral periaqueductal gray (vPAG), or sham lesions. Rats were placed adjacent to a compartment containing a cat. Sham-lesioned rats avoided the area nearest the cat and preferred the area furthest away from the cat. They also exhibited numerous defensive responses including, climbing, escape from the apparatus, and freezing. Rats with lesions of the ACe reacted like the sham lesioned rats by preferring the area of the apparatus furthest from the cat, however they climbed and escaped significantly less than sham lesioned rats. Avoidance of the area adjacent to the cat was attenuated in rats with lesions of the vPAG. Climbing along the walls of the apparatus was also attenuated in rats with lesions of the vPAG. Escapes from the apparatus were not significantly reduced by lesions of the vPAG and dlPAG. Thus, ACe lesions attenuated climbing and eliminated escapes, but did not impair locomotion of the rat away from the cat.     

A Reply to McDonald: A Defense in Favor of Requirement Conflicts

In "The Presumption in Favor of Requirement Conflicts" Julie McDonald has offered some serious and challenging criticisms of the recent literature centered around the moral dilemmas debate. If McDonald is correct, the philosophers who have contributed to this debate share some questionable presuppositions about the role and significance of an adequate moral theory. It is beyond dispute that the moral dilemmas debate has elevated the importance of requirement conflicts above other types of conflicts. McDonald argues that this is a needlessly restrictive way to approach the issue. She maintains that the potential for unavoidable moral residue in the form of guilt, as well as the chance of moral unresolvability, are the two central concerns which motivate the issue. These concerns then figure into her diagnosis of the implicit background assumptions that explain the rationality of the debate. In what follows I shall consider whether or not the participants to this debate are forced to accept these assumptions.     

Fear and Anxiety: Possible Roles of the Amygdala and Bed Nucleus of the Stria Terminalis

This paper presents a provisional classification of deliberate strategies for improving unpleasant affect based on conceptual judgements concerning their similarities and differences. A corpus of self-reported upward affectregulation strategies was collected using questionnaires, interviews, and group discussions, in conjunction with an examination of existing literature on related topics. A total of 162 distinct strategies were identified and a preliminary categorisation was developed by the investigators. We then conducted a card-sort task in which 24 participants produced separate classifications of the strategies. The similarity matrix arising from co-occurrence data was subjected to hierarchical cluster analysis and the obtained typology provided independent support for our proposed distinctions between strategies implemented cognitively and behaviourally, between diversion and engagement strategies, and between active distraction and direct avoidance, and for specific lower-level groupings of strategies relating to venting, reappraisal, and seeking social support. Potential refinements and applications of the resulting classification system are considered.     

The Effects of Selective Cholinergic Basal Forebrain Lesions and Aging upon Expectancy in the Rat

The effects of selective cholinergic cell loss within the basal forebrain (BF) were determined using a task that requires shifting of attention between two visual stimuli. Discriminability between two stimuli and response bias were determined in young and old F-344 rats given BF injections of IgG-192 saporin (100 ng). The lesion reduced ChAT activity in the frontal and parietal cortices, hippocampus, and olfactory bulbs. The lesion did not significantly alter Na⁺/K⁺-ATPase activity in cortex, hippocampus, or olfactory bulbs, or endogenous levels of neuropeptide Y and neurokinin B within the BF. The BF lesions impaired both stimulus discriminability and response bias in young and old rats. The BF lesions had a significantly greater effect upon stimulus discriminability and response bias in aged rats, compared to young rats, only when the stimulus duration was very brief, i.e., when the task was most difficult to solve. At longer stimulus durations, aging and lesions showed no interaction. The results suggest that the selective loss of cholinergic cells in the BF, but not normal aging, impairs the ability to discriminate between independent sensory stimuli. The loss of these cells confers a response bias in simple operant tasks involving motor responses to reward-related visual stimuli.     

Implications of Cybernetic Epistemology for Clinical Research: A Reply to Howard

This response to Howard's article deals with the application of cybernetic epistemology to clinical research and practice. Implications for scientific research are discussed.     

The Role of the Amygdala and the Ventromedial Prefrontal Cortex in Emotional Regulation: Implications for Post-traumatic Stress Disorder

Neuropsychology Review - The importance of the amygdala as a salience detector and in emotional learning is now well accepted. The mechanisms that regulate and inhibit the amygdala, however, are...     

Recall,recognition, and the hippocampus: Reply to Yonelinas et al. (2004)

Two recent studies disagree about whether recall is more impaired than recognition (and recollection more than familiarity) in patients with damage limited to the hippocampus (Manns, Hopkins, Reed, Kitchener, & Squire, 2003; Yonelinas et al., 2002). Wixted and Squire (2004) pointed out that the disagreement about recall and recognition stems entirely from an outlying recognition score obtained by 1 of 55 control subjects in Yonelinas et al. (2002). In their comment on our paper, Yonelinas et al. (2004) minimize the importance of this result and argue that the role of the hippocampus in recollection and familiarity is best studied using different methods that attempt to measure these processes directly. Here, we argue that the recall versus recognition comparison is the strongest test because it relies on the fewest controversial assumptions, and that the other approaches explored by Yonelinas et al. (2002) rely on questionable, theory-laden assumptions. We also rehearse the reasons for concluding that the patients studied by Manns et al. (2003) have damage limited to the hippocampal region (hippocampus proper, dentate gyrus, and subiculum), and we emphasize that important questions remain about the patients studied by Yonelinas et al. (2002), inasmuch as no neuroanatomical information and minimal neuropsychological information has been provided.     

Flickers of Freedom and Modes of Action: A Reply to Timpe

In recent years, many incompatibilists have come to reject the traditional association of moral responsibility with alternative possibilities. Kevin Timpe argues that one such incompatibilist, Eleonore Stump, ultimately fails in her bid to sever this link. While she may have succeeded in dissociating responsibility from the freedom to perform a different action, he argues, she ends up reinforcing a related link, between responsibility and the freedom to act under a different mode. In this paper, I argue that Timpe’s response to Stump exploits concessions she need not have made. The upshot is that, contrary to what Timpe maintains, there is no reason to doubt that Stump's brand of incompatibilism is a genuine alternative to the traditional variety.

The Critical Role of Cholinergic Basal Forebrain Neurons in Morphological Change and Memory Encoding: A Hypothesis

It has been known for a long time that cholinergic basal forebrain neurons which project to the cerebral cortex play a role in learning and memory. Behavioral studies following lesions, for example, repeatedly have suggested multiple learning-related roles for these neurons. Apart from behavioral studies, cholinergic neurons have been shown to possess extraordinarily plastic axons. This plasticity has not been related comprehensively to mnemonic devises, even though morphological changes in the CNS are prime candidates for the neural engram. In this paper, I propose a hypothesis that relates these two characteristics of cholinergic neurons. This hypothesis is that plastic cholinergic axon terminals induce structural reorganization in their targets during memory storage. Possible intracellular mechanisms are examined, whereby acetylcholine release in the cerebral cortex could cause postsynaptic structural changes. Finally, the characteristics of the overall cholinergic–cholinoceptive cell “engram” are elaborated with particular attention paid to the encoding of the stimulus properties along with the context and meaning of the stimulus.     

Motivation to Lead: Research on the Motives for Undertaking Leadership Roles in the Israel Defense Forces (IDF)

Sustained flight operations are likely to produce fatigue and performance decrement in aviators. We assessed changes in cognitive performance using a workhest schedule modeled on successive long-range attack missions. Twelve subjects performed several subtests of the Unified Tri-Service Cognitive Performance Assessment Battery and the Walter Reed Performance Assess- ment Battery 18 times during a simulated sustained operation. The scenario consisted of a 9-hr planning session followed by a 4-hr rest period and a 14-hr daytime mission. After 6 hr of rest, subjects repeated this schedule with a nighttime mission. For two spatial tests, subjects showed linear increases in response rate and one of its components, error rate. Subjects appeared to change strategy as the study progressed, possibly exchanging a higher failure rate for a savings in time. Any tendency to take chances when fatigued may have serious implications for aircrew in sustained operations.     

In Defense of the Asymmetric Convergence Model of Public Justification: A Reply to Boettcher

This piece defends the asymmetric convergence model of public justification in response to James Boettcher’s critique. I maintain both that Boettcher’s critique of asymmetric convergence fails and that his alternative view, Weak Public Justification, faces a number of serious challenges.     

Subjective measures of implicit knowledge that go beyond confidence: Reply to Overgaard et al.

Overgaard, Timmermans, Sandberg, and Cleeremans (2010) ask if the conscious experience of people in implicit learning experiments can be explored more fully than just confidence ratings allow. We show that confidence ratings play a vital role in such experiments, but are indeed incomplete in themselves: in addition, use of structural knowledge attributions and ratings of fringe feelings like familiarity are important in characterizing the phenomenology of the application of implicit knowledge.     

Reply to Hauck, et al. concerning nonsexual household transmission of HIV in Zaire

CDC researchers mishandle statistical evidence and overstate case against casual transmission of HIV. Reassessment by Hauck, et al. is statistically inappropriate.     

Hemisphericsymmetries in the identification of band-pass filtered letters Reply to Christman et al. (1997)

Christman, Kitterle, and Niebauer (1997) have examined the hypothesis that the two cerebral hemispheres are specialized for processing different ranges of spatial frequency. Their two experiments partially replicated an experiment of Peterzell, Harvey, and Hardyck (1989), who used Sergent's (1982) letter identification paradigm with spatial-frequency band-pass filtered letters as stimuli. We acknowledge the unusual strengths of Christman et al.'s experiments, but argue that the results support the original conclusion of Peterzell et al.: The results are not attributable to hemispheric asymmetries in spatial frequency processing.     

Critical Evaluation of Porter et al.'s Organizational Commitment Questionnaire: Implications for Researchers

Organizational commitment is a useful construct for understanding employee behavior. The Organizational Commitment Questionnaire (Porter et al. 1974) has been used extensively to operationalize this construct, but its dimensionality is unclear. The present work assesses the dimensionality of the OCQ using two sales force samples.