PubMed Health⌕ Search

Biomedical subjects

A G Baker

Publications and source records attributed to A G Baker.

At least 19 recordsLinked to original sources
PubMed1998

Lesions of the hippocampus or fornix do not interfere with the relative validity effect on a discrete stimulus or the context.

Two experiments with rats used an appetitively motivated instrumental discrimination procedure to examine whether damage to the hippocampal system would interfere with the relative validity effect in which a partially reinforced stimulus trained in compound acquires a weak conditioned response when concurrently trained CSs are perfect predictors of the presence or absence of the US [A.R. Wagner, F.A. Logan, K. Haberlandt, T. Price, Stimulus selection in animal discrimination learning, J. Exp. Psychol. 76 (1968) 171-180]. The true discrimination (TD) group received training with two compound cues containing a common element. One compound was reinforced and another never reinforced (AX+, BX-). Following TD training the common element (X) failed to acquire a strong conditioned response in comparison to a control, pseudo discrimination (PD) group (AX+/-, BX+/-), in which both compound cues were reinforced 50% of the time. Although (X) was reinforced on a partial reinforcement schedule, (50%) in both groups, conditioning of X was affected by the reinforcement schedules of the accompanying elements (A and B). Neither radio-frequency lesions of the fornix-fimbria (Experiment 1) nor neurotoxic lesions of the hippocampus (Experiment 2) interfered with this effect on X or on the same effect found during the inter trial interval (ITI). Rates of ITI responding were higher in the PD groups than in the TD groups suggesting stronger contextual conditioning following PD training. Furthermore, disruptions to the hippocampal system in Experiment 2 resulted in increased rates of lever pressing for food. These results do not support the notion that the hippocampus is critically involved in selective associations.

Animals↗
PubMed1997

The use of osazones as matrices for the matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates.

Fifteen sugar osazones were synthesized and evaluated for their use as matrix-assisted laser desorption/ ionization matrices. Various carbohydrate samples were analyzed, indicating that D- or L-arabinosazone, prepared from D- or L-arabinose and phenylhydrazine, gave the overall best performance. The arabinosazones facilitated superior analyses in providing a highly uniform distribution of sample molecules within the matrix microcrystals, and a possibility of using low laser energy for irradiation, leading to high spectral resolution and low matrix background. The arabinosazones with a moderate content of sodium ions promoted specific fragmentation for certain carbohydrates tested. The 50 fmol amounts of maltohexaose and maltoheptaose (present in 0.1 microliter of sample/matrix solution) were detected at a signal-to-background ratio of 3:1.

Arabinose↗
PubMed1997

Systematic comparison of the effects of hippocampal and fornix-fimbria lesions on acquisition of three configural discriminations.

The effects of lesions to the hippocampal system on acquisition of three different configural tasks by rats were tested. Lesions of either the hippocampus (kainic acid/colchicine) or fornix-fimbria (radiofrequency current) were made before training. After recovery from surgery, rats were trained to discriminate between simple and compound-configural cues that signaled the availability or nonavailability of food when a bar was pressed. When positive cues were present, one food pellet could be earned by pressing a lever after a variable time had elapsed. The trial terminated on food delivery (variable interval 15 s). This procedure eliminates some possible alternative explanations of the results of previous experiments on configural learning. Hippocampal lesions increased rates of responding and retarded acquisition of a negative patterning task (A+, B+, AB-); using a ratio measure of discrimination performance these lesions had a milder retarding effect on a biconditional discrimination (AX+, AY-, BY+, BX-), and they had no effect on a conditional context discrimination (X: A+, B-; Y: A-, B+). Fornix-fimbria lesions did not affect acquisition of any of these tasks but increased rates of responding. The results suggest that several task parameters determine the involvement of the hippocampus in configural learning; however, all tasks tested can also be learned to some extent in the absence of an intact hippocampal system, presumably by other learning/memory systems that remain intact following surgery. The lack of effect of fornix-fimbria lesions on any of these tasks suggests that retrohippocampal connections with other brain areas may mediate hippocampal contributions to the learning of some configural tasks. An analysis of these results and of experiments on spatial learning situations suggests that involvement of the hippocampus is a function of the degree to which correct performance depends on a knowledge of relationships among cues in a situation.

Animals↗
PubMed1997

Modification of horse heart cytochrome c with trans-2-hexenal.

Horse heart cytochrome c reacting with trans-2-hexenal was used as a simple model of the nonspecific interactions of proteins with 2-alkenals. The reaction mixtures containing relatively high concentrations of the protein and aldehyde were characterized using visible spectrophotometry, fluorescence, and circular dichroism measurement, capillary isoelectric focusing, size-exclusion chromatography, polyacrylamide gel electrophoresis, and mass-spectrometric techniques. The mass-spectrometric data indicate that cytochrome c becomes modified with one or two molecules of hexenal as the major reaction product. The modified species with a correspondingly lowered isoelectric point were detected through capillary isoelectric focusing. The results of proteolytic studies indicate nonspecific modifications. Significant quantities of the oligomeric forms of hexenal-modified protein were also observed electrophoretically.

Aldehydes↗
PubMed1996

Infected iliac pseudoaneurysm after uncomplicated percutaneous balloon angioplasty and (Palmaz) stent insertion: a case report and literature review.

Percutaneous balloon angioplasty and endovascular stent placement are becoming common techniques intended to reduce the need for surgical bypass procedures that may be more expensive or have higher morbidity rates. Prophylactic antibiotics are not currently used before stent placement in most centers even when implanted via the femoral route. Infectious complications have been rare. In the case presented here an infected common iliac pseudoaneurysm occurred after percutaneous balloon angioplasty and stent placement. The literature is reviewed.

Aneurysm, False↗
PubMed1995

Effects of reward and response costs on inhibition in ADHD children.

This study examined effects of reward and response costs on the ability of 19 attention-deficit hyperactivity disorder (ADHD) and 17 control children to inhibit responding. Children were tested under 4 reinforcement conditions on a go/no-go learning task developed by J. P. Newman, C. S. Widom, and S. Nathan (1985). Two conditions involved both reward and response costs. 1 response costs only, and 1 reward only. ADHD children made more commission errors than controls across the 4 conditions. Analyses of learning curves indicated that group differences became larger on later trials. Thus, impaired inhibition was more generalized in ADHD children than in the psychopaths and extraverts studied by Newman and colleagues, and it became most evident when the children were required to improve learning across trials.

Attention Deficit Disorder with Hyperactivity↗
PubMed1986

Some effects of early monocular deprivation in the Mongolian gerbil.

The effects of short- and long-term early monocular deprivation were investigated in 4 Mongolian gerbils using interocular differences in grating acuity as a measure of deprivation-induced impairment. All gerbils showed acuity deficits in the initially deprived eye, ranging in magnitude from 0.24-1.40 octaves. One month of monocular deprivation from eye opening proved sufficient to induce a permanent acuity impairment.

Animals↗
PubMed1985

Latent inhibition, habituation, and sensory preconditioning: a test of priming in short-term memory.

Four experiments tested priming in short-term memory as a model for latent inhibition and habituation. The model postulates that the two phenomena results from reduced processing when a representation of the target stimulus is already active (primed) in short-term memory at the time of its presentation. Priming is assumed to depend on the integrity of an association formed between the contextual stimuli and the conditional stimulus (CS) during exposure. Using a procedure that should have overshadowed the context, Experiment 1 found that latent inhibition and habituation were nevertheless maintained when a second CS of either equal or shorter duration overlapped with the target during exposure. Experiments 2, 3, and 4 showed that sensory preconditioning as well as habituation and latent inhibition were obtained with compound exposure, providing reasonable evidence that the added CS was indeed processed along with the target during exposure. These results are interpreted as being inconsistent with the priming model.

Animals↗
PubMed1983

Grating acuity of the Mongolian gerbil (Meriones unguiculatus).

The grating acuity of the Mongolian gerbil was measured using a two-alternative forced-choice task in a jumping stand. Frequency-of-seeing curves generated by a modified method of limits indicated that the acuity of the gerbil for a horizontal square-wave grating is about 1.5-2.0 cycles/degree (c/deg) at 70 cd/m2, using the 70%- and 80%-correct levels of performance as criteria for defining acuity. The acuity for horizontal gratings is reliably better than that for vertical gratings, and this difference does not appear to be luminance-dependent. A corresponding orientation anisotropy is not seen in acquisition scores, nor is an 'oblique effect' evident. The acuity of the gerbil continues to increase with luminance into the (human) photopic range, suggesting the existence of a functional cone system. The gerbil visual system appears to be well adapted for detail vision in a diurnal lifestyle.

Animals↗
PubMed1982

Pain, control over treatment, and compliance in dialysis and transplant patients.

Pain was surveyed via structured interview and the McGill Pain Questionnaire in 53 dialysis and 27 transplant patients. Increased patient control over the dialysis procedure was not associated with a reduction in pain though perceived control may have been. Compliance with the dialysis regimen did not predict pain and the validity of the category "dialysis headache" was questioned. Overall, transplant recipients did not report significantly less pain than dialysis patients. Self-reported depression was correlated positively with pain. The clinical implications of these findings are discussed.

Adult↗
PubMed1981

Contextual conditioning and the US preexposure effect in conditioned fear.

A series of five experiments was carried out in which fear of context caused by exposure to shocks was manipulated by signaling the shocks with a discrete stimulus, signaling the days during which shocks occurred with a session-long stimulus, or switching the context between exposure and the subsequent test. All these manipulations influenced fear of the context in the manner predicted by the Rescorla-Wagner associative model. Following this, all the rats were given conditioning trials with shock and a different discrete stimulus. All preexposure treatments produced consistent and reliable interference with conditioning with the exception of signaling the shocks with a discrete stimulus, which greatly reduced interference. These results are interpreted as being consistent both with a cognitive explanation of the US exposure effect, which claims that animals learn that shocks are unpredictable during conditioning and this knowledge retards future conditioning when they are predictable, and with an adaptation explanation, which claims that unpredictable shocks produce chronic fear and this fear through either a change in adaptation level or through emotional exhaustion renders the shocks less reinforcing during the conditioning test.

Adaptation, Psychological↗