Analysis of two methods of isometric muscle contractions during the anti-G straining maneuver

This study investigated the difference in Mean Arterial Pressure (MAP) and Cardiac Output (CO) between two methods of isometric muscle contractions during the Anti-G Straining Maneuver (AGSM). 12 subjects (ages 18 to 38 yrs, height 176.8 +/- 7.4 cm, body mass 78.8 +/- 15.6 kg, percent body fat 14.3 +/- 6.6%) participated in the study. The study was a one-way within-subject design with test conditions counterbalanced. Two methods of isometric muscle contractions lasting 30 seconds each were assessed; an isometric push contraction and an isometric muscle tensing contraction. The dependent parameters were MAP and CO. The average MAP during the push contraction was 123 mmHg, SD +/- 11 and for tense was 118 mmHg, SD +/- 8. CO was 7.6 L/min, SD +/- 1.6 for push and 7.9 L/min, SD +/- 2.0 for tense method. Dependent t-tests revealed t(11) = 1.517, p = 0.157 for MAP and t(11) = 0.875, p = 0.400 for CO. This study demonstrated that the two methods of isometric muscle contractions were not statistically different with regards to MAP and CO. Therefore, both forms of isometric contractions may be potentially useful when performing the muscle contraction portion of the AGSM

Basal forebrain activation enhances cortical coding of natural scenes

The nucleus basalis (NB) of the basal forebrain is an essential component of the neuromodulatory system controlling the behavioral state of an animal, and it is thought to play key roles in regulating arousal and attention. However, the effect of NB activation on sensory processing remains poorly understood. Using polytrode recording in rat visual cortex, we show that NB stimulation causes prominent decorrelation between neurons and marked improvement in the reliability of neuronal responses to natural scenes. The decorrelation depends on local activation of cortical muscarinic acetylcholine receptors, while the increased reliability involves distributed neural circuits, as evidenced by NB-induced changes in thalamic responses. Further analysis showed that the decorrelation and increased reliability improve cortical representation of natural stimuli in a complementary manner. Thus, the basal forebrain neuromodulatory circuit, which is known to be activated during aroused and attentive states, acts through both local and distributed mechanisms to improve sensory coding

The neuronal base of perceptual learning and skill acquisition

Sensory systems represent an essential interface between the organism and its environment. Throughout life the organism continuously interacts with stimuli, objects and environments and this interaction has a long-lasting effect on its cen-tral nervous system. Humans learn to respond optimally to stimuli as they occur in everyday scenarios. The neuroscience of learning and memory attempts to explain how the nervous system adapts to new environments and learns through repeated practice. Two forms of learning have been the focus of neuroscientific investiga-tion: procedural learning and perceptual learning. Procedural learning is defined as a training-induced change in performance for a given task, in which repeating a complex activity leads to an automatic (and often unconscious) production of highly adaptive behaviour or skill. Perceptual learning, on the other hand, is “the specific and relatively permanent modification of perception and behaviour following sensory experience. It encompasses parts of the learning process that are independent from conscious forms of learning and involve structural and/or functional changes in primary sensory cortices” (Fahle & Poggio, 2002). These two forms of learning are involved in skill acquisition and they underlie at least partly the formation of professional expertise. This chapter will introduce concepts in neuroscience required to understand the possible changes that occur in biological nervous systems when an organism is re-peatedly exposed to a particular stimulus configuration. The focus in this chapter will be on low-level processes in perception and motor control and how these low-level processes are improved by learning. More complex cognitive skills that build on these low-level processes will be discussed in the final section of this chapter. To introduce the reader to concepts used in neuroscience (see glossary below), processes like adaptation, habituation, sensitization, conditioning and extinction will be defined and differentiated from procedural and perceptual learning. Each of these processes exhibits specific time constants that describe the change in neu-ral activity over time, being either short- or long-term. These low-level forms of learning are discriminated from other forms of learning and memory that require conscious encoding, consolidation and recall. Next, a review is given of the most relevant work on the topics of perceptual and procedural learning. Some recent insights into the role of dopaminergic and cholinergic processes will be given. The chapter will conclude by providing a description of the state of the art in the neu-roscientific study of skill acquisition. A discussion of the possible ramifications of this research on the design of learning environments will be given