Search

This study evaluated whether apraxia can be understood as due to impaired motor representations or motor imagery necessary for appropriate object-use, imitation, and pantomime. The causal role of the left inferior parietal lobe (IPL), which is heavily implicated in apraxia, is also evaluated. These processes are appraised in light of the proposed ventro-dorsal sub-stream of the classic two visual pathway model, where perceptual information from the ventral stream and the dorsal action stream are integrated and essential for object manipulation. Using a task assessing object-use perception, stroke patients with apraxia demonstrated a selective deficit during perceptual decisions reliant on the integration of visible and known object properties to select the appropriate grasp for object-use. This deficit increased with apraxia severity. A dissociation was evident in these patients showing intact non-motoric perceptual decisions regarding the functional semantic relationship between two objects in the absence of the actor (e.g. how a hammer hits a nail). Converging evidence was found using a modified version of the same task in a neuromodulation study that directly targeted the left IPL in healthy participants using transcranial direct current stimulation (tDCS). Application of inhibitory stimulation over the left IPL reduced performance during perceptual decisions regarding object manipulation whilst performance was unaffected during functional semantic decisions. Excitatory stimulation of the left IPL did not affect performance in either task. Combined, these results suggest that the left inferior parietal lobe is critical for motor imagery, and that apraxia may be caused by an inability to use internal motor representations of object manipulation. These results are discussed in terms of motoric and non-motoric perceptual processes and the proposal of an additional ventro-dorsal sub-stream within the dorsal and ventral visual pathways model. [ABSTRACT FROM AUTHOR]

Abstract: Optic ataxic patients have deficits in the visual control of manual reaching and grasping. It has been established previously that these deficits in target-directed behaviour improve following a delay in response. Recently it has been demonstrated that optic ataxic patients also have deficits in taking potential obstacles into account during reaching. The present study was therefore designed to test whether delay would bring an improvement in this behaviour as well. We present experimental data from a patient with unilateral optic ataxia (M.H.). First we document M.H.''s pointing errors, which show a reliable pattern of impairment when pointing to targets in his right visual field, particularly when using his right hand. We then show that a similar pattern of deficits is observable in his ability to negotiate between non-targets: that is, M.H. selectively fails to take account of obstacles in his right visual field, but only while reaching with his right hand. Finally we demonstrate that this obstacle avoidance deficit disappears following a 5s delay in response: under these conditions M.H. now takes account of both non-target objects with either hand. The results are interpreted within the ‘two visual streams’ model of cortical visual processing. [Copyright &y& Elsevier]

Recent advances in our understanding of induced responses in plants and their regulation, brought about by a revolution in molecular biology, have re-focused attention on the potential exploitation of endogenous resistance mechanisms for crop protection. The future goal of crop biotechnology is thus to engineer a durable, multimechanistic resistance to insect pests through an understanding of the diversity of plant responses to insect attack. [Copyright &y& Elsevier]

The mannose-specific snowdrop lectin (Galanthus nivalis agglutinin: GNA), when fed to insects, binds to the gut epithelium and passes into the haemolymph. The ability of GNA to act as a carrier protein to deliver an insecticidal spider venom neurotoxin (Segestria florentina toxin 1: SFI1) to the haemolymph of lepidopteran larvae was investigated. Constructs encoding SFI1 and an SFI1/GNA fusion protein were expressed in Pichia pastoris. The insecticidal activity of purified recombinant proteins on injection was found to be comparable to published values for SfI1 purified from spider venom [Toxicon 40 (2002) 125]. Whereas neither GNA nor SFI1 alone showed acute toxicity when fed to larvae of tomato moth (Lacanobia oleracea), feeding SFI1/GNA fusion at 2.5% of dietary proteins was insecticidal to first stadium larvae, causing 100% mortality after 6 days. The protein also showed a significant, dose dependent, toxicity towards fourth and fifth stadium larvae, with growth reduced by up to approximately 90% over a 4-day assay period compared to controls. Delivery of intact SFI1/GNA to the haemolymph in these insects was shown by western blotting; haemolymph samples from fusion-fed larvae contained a GNA-immunoreactive protein of the same molecular weight as the SFI1/GNA fusion. SFI1/GNA and similar fusion proteins offer a novel and effective approach for delivering haemolymph active toxins by oral administration, which could be used in crop protection by expression in transgenic plants. [Copyright &y& Elsevier]

[Display omitted] • Highlights potential aphid control by targeting endosymbiont (B. aphidicola) genes. • Genes in B. aphidicola biosynthetic pathways respond to omission of multiple EAAs. • A. pisum survival decreased significantly on sub-optimal ilv- and thrA- diets. • B. aphidicola gene expression increased significantly with sub-optimal A. pisum nutrition. The endosymbiotic bacterium Buchnera aphidicola allows its host Acyrthosiphon pisum to utilise a nutritionally limited phloem sap diet without significant mortality by providing essential amino acids (EAAs), which it biosynthesises de novo via complex pathways consisting of multiple enzymes. Previous studies have reported how non-essential amino acids (NEAAs) provided by the host are utilised by B. aphidicola , along with how genes within the biosynthetic pathways respond to amino acid deficiency. Although the effect on B. aphidicola gene expression upon the removal of a single EAA and multiple NEAAs from the A. pisum diet has been reported, little is known about the effects of the complete simultaneous removal of multiple EAAs, especially branched-chain amino acids (BCAAs). To investigate this, A. pisum was provided with amino acid deficient diets ilv- (lacking isoleucine, leucine, valine) or thra- (lacking threonine, methionine, lysine). Due to their involvement in the production of several amino acids, the expression of genes ilvC , ilvD (both involved in isoleucine, leucine and valine biosynthesis) and thrA (involved in threonine, methionine and lysine biosynthesis) was analysed and the expression of trpC (involved in tryptophan biosynthesis) was used as a control. Survival was reduced significantly when A. pisum was reared on ilv- or thra- (P < 0.001 and P = 0.000 respectively) compared to optimal artificial diet and was significantly lower on ilv- (P < 0.001) than thra-. This is likely attributed to the EAAs absent from ilv- being required at higher concentrations for aphid growth, than those EAAs absent from thra-. Expression of ilvC and ilvD were upregulated 2.49- and 2.08-fold (respectively) and thrA expression increased 2.35- and 2.12-fold when A. pisum was reared on ilv- and thra- (respectively). The surprisingly large upregulation of thrA when reared on ilv- is likely due to threonine being an intermediate in isoleucine biosynthesis. Expression of trpC was not affected by rearing on either of the two amino acid deficient diets. To our knowledge this study has shown, for the first time, how genes within the biosynthetic pathways of an endosymbiont respond to the simultaneous complete omission of multiple EAAs as well as all three BCAAs (leucine, isoleucine, valine), from the host diet. [ABSTRACT FROM AUTHOR]

The action observation network has been proposed to play a key role in predicting the action intentions (or goals) of others, thereby facilitating social interaction. Key information when interacting with others is whether someone (an agent) is moving towards or away from us, indicating whether we are likely to interact with the person. In addition, to determine the nature of a social interaction, we also need to take into consideration the distance of the agent relative to us as the observer. How this kind of information is processed within the brain is unknown, at least in part because prior studies have not involved live whole-body motion. Consequently, here we recorded mobile EEG in 18 healthy participants, assessing the neural response to the modulation of direction (walking towards or away) and distance (near vs. far distance) during the observation of an agent walking. We evaluated whether cortical alpha and beta oscillations were modulated differently by direction and distance during action observation. We found that alpha was only modulated by distance, with a stronger decrease of power when the agent was further away from the observer, regardless of direction. Critically, by contrast, beta was found to be modulated by both distance and direction, with a stronger decrease of power when the agent was near and facing the participant (walking towards) compared to when they were near but viewed from the back (walking away). Analysis revealed differences in both the timing and distribution of alpha and beta oscillations. We argue that these data suggest a full understanding of action observation requires a new dynamic neuroscience, investigating actual interactions between real people, in real world environments. • When watching a person approach or walk away, the action observation network is tuned both to proximity and action direction. • Dissociable cortical patterns of alpha and beta reveal that socially relevant cues modulate the action observation network. • Naturalistic EEG data confirms the need for new methods to better understand real life interactions between people. [ABSTRACT FROM AUTHOR]

Abstract: Transcranial magnetic stimulation (TMS) has been used widely in research investigating corticospinal (CS) excitability during action observation. Generally, this work has shown that observation of an action performed by others, in the absence of overt movement, modulates the excitability of the CS pathway in humans. Despite the extent of the literature exploring action observation effects, however, there has been little research to date that has compared observation with the combination of observation and execution directly. Here, we report a single-pulse TMS study that investigated whether CS excitability during action observation was modulated by actions performed by the observers prior to viewing a ball pinching action. The results showed that CS excitability during action observation increased when compared to observation of a static hand, but that there was no additional motor facilitation when participants performed the same action prior to observing it. Our findings highlight the importance of action observation and its consequences on the CS system, whilst also illustrating the limited effect of prior action execution on the CS pathway for a simple action task. [Copyright &y& Elsevier]