Search PubMed⌕ Search

Biomedical subjects

A Sahgal

Publications and source records attributed to A Sahgal.

At least 73 records · Page 4Linked to original sources
PubMed1983

The effects of inferotemporal cortex lesions on Konorski delayed pair comparison in monkeys.

Rhesus monkeys were trained on a pair comparison recognition memory task, running concurrently with a signal detection (attention) problem. The animals were given bilateral posterior or anterior inferotemporal cortex lesions once satisfactory performance had been reached. The former group sustained attentional but only transient mnemonic impairments. Anterior lesions impaired visual learning and memory, but not attention. We confirm that inferotemporal cortex is sub-divided into at least two distinct regions, serving visual attention and other cognitive processes. The role of inferotemporal cortex in recognition memory is discussed, and it is concluded that task-related problems do not permit an unambiguous resolution of this question.

Animals↗
PubMed1983

Central administration of thyrotropin-releasing hormone and histidyl-proline-diketopiperazine disrupts the acquisition of a food rewarded task by a non-aversive action.

The effects of thyrotropin-releasing hormone (TRH) and its metabolites on operant behaviour have rarely been explored. In this study, the effects of intracerebroventricular (icv) administration of TRH and histidyl-proline-diketopiperazine (DKP), a metabolite of TRH, on the acquisition of a food-rewarded lever-press task were compared with saline-treated controls. TRH and DKP severely retarded the acquisition of lever pressing. The effects of systemically administered D-amphetamine were also examined in order to test whether this result was due to any stimulant properties of these peptides. These results suggest that stimulatory effects do not adequately account for impaired acquisition. The possibility that the disruption of learning was due to an aversive effect of icv administration of these peptides was tested by means of a conditioned place paradigm. Neither peptide induced an avoidance of the environment with which it had previously been paired. Several possible reasons for the peptides' adverse effect on learning are discussed, including the possibility that TRH and DKP act on attentional mechanisms.

Animals↗
PubMed1983

Vasopressin retards the acquisition of positively reinforced lever pressing in homozygous Brattleboro rats.

Previous studies have indicated that vasopressin treatment improves the poor performance of congenitally vasopressin deficient (Brattleboro) rats on shock avoidance paradigms, an effect thought to relate to the peptide's enhancement of mnemonic processing. In the present study, a food rewarded autoshaping task was used to study the acquisition, retention, extinction and subsequent re-acquisition of lever pressing. Vasopressin (1 microgram/rat, subcutaneous) was found to impair acquisition in these animals. The possibility that this deleterious effect was due to a transient suppression of motor capability was tested in a second experiment. Vasopressin increased overall locomotor activity levels, but there was an indication that rates immediately following injection were lower than usual. An explanation for the effects of vasopressin based on arousal enhancement is discussed, and it is suggested that the neuropeptide may be concerned with the regulation of arousal and hence performance.

Animals↗
PubMed1983

The effects of thyrotropin-releasing hormone, metabolites and analogues on locomotor activity in rats.

Thyrotropin-releasing hormone (TRH) has generally been reported to increase locomotor activity in rats; however there are also some negative reports. In order to identify the possible causes for this discrepancy, the effects of intra-cerebroventricular injection of TRH, its metabolites 'acid TRH' (TRH-OH) and His-Pro-diketopiperazine (DKP), and two analogues 3-methyl-His-TRH and RX 77368 (3,3-dimethyl-Pro-TRH), were assessed using photocell activity cages. All compounds were tested in groups of eight rats in the afternoon (1300-1700 h), but in addition TRH and DKP were tested in two further groups of rats during the morning (0900-1230 h). TRH and DKP failed to induce a significant rise in activity during the morning test period, but TRH did have a significant effect when tested in the afternoon. Both TRH and TRH-OH caused dose dependent increases in locomotor activity, whereas DKP and the two analogues had no effect. This stimulation of activity was shown to be at least partly mediated by dopamine since locomotor enhancement was blocked in a second experiment using the dopamine antagonist alpha-Flupenthixol. The results are discussed in terms of actions on the mesolimbic dopamine system, and the importance of circadian variations within this system to the expression of peptide effects in general.

Animals↗
PubMed1982

Failure of vasopressin to enhance memory in a passive avoidance task in rats.

Several authors have suggested that the neurohypophysial hormone arginine-8-vasopressin (AVP) facilitates both the consolidation and the retrieval of memory. This conclusion has relied mainly on the finding that AVP increases the latency of re-entry into a box where shock has previously been encountered, that is, in a passive avoidance task. Our results do not support this interpretation. On the contrary, we found that post-trial, intraventricular (i.t.) administration of AVP (1 ng in 1 microliter) produced relatively short as well as long latencies (a bimodal effect), suggesting that the peptide acts on motivational processes, for example by increasing arousal.

Animals↗
PubMed1980

Amylobarbitone and forgetting.

In an earlier report (Hulme et al. 1979), we argued that sodium amylobarbitone (SAB) affects the acquisition of information. That conclusion was based on the finding that SAB produces rates of forgetting that are similar to control, thereby ruling out storage (and possibly retrieval) deficiencies which would predict dissimilar rates. However, it is possible that the rate of forgetting is itself influenced by the amount of information that actually entered store in the first place, and SAB reduces this by affecting acquisition. The possibility that both acquisition and storage could therefore have been affected was explored by equating control and drug zero delay performance, which was achieved by lowering the performance of control subjects. Nonetheless, subsequent rates of forgetting remained similar, thereby strengthening the acquistion hypothesis.

Amobarbital↗
PubMed1980

Ethanol affects the acquisition of information.

Two experiments were carried out on pigeons to assess the effects of acute ethanol (ETOH) administration on a delayed pair comparison procedure. ETOH disrupted performance at the two higher doses (1.0 and 2.0 g/kg, given orally). When the initial (zero delay) performance levels of treated and untreated birds were equated by (indirectly) varying the to-be-remembered stimulus' exposure duration, it was found that the impairment could, to a point, be overcome. This finding is interpreted in terms of hypothesis which suggests that ETOH affects the acquisition but not the subsequent storage of information.

Animals↗
PubMed1980

Recognition memory, chlordiazepoxide and rhesus monkeys: some problems and results.

Monkeys were taught a variation of the Konorski [26] pair comparison task, with and without delay, by first training them on a 'simultaneous' procedure involving the judicious use of both correction and non-correction training. In this task, they had to respond to a left hand panel if two simultaneously present colour (green or red) stimuli were the same (e.g. green, green) and to a right hand panel if they were different (e.g. red, green). Once they had learned this task, delays ranging from 0 to 16 sec were interposed between the two stimuli, and reliable forgetting curves were obtained. The effects of chlordiazepoxide (CDP) on such behaviour were assessed in the next experiment. Few impairments were observed even after high (80 mg/kg, i.p.) doses of the drug, and this is in contrast to our previously reported findings with pigeons [31]. However, it was argued that the stimulus presentation times could have been too long, thereby enabling the animal to overcome any deficiency in mnemonic processing. This problem was tackled in the third experiment, by presenting the to-be-remembered stimulus for brief periods; in addition, signal detection performance was also assessed. In spite of such refinements, CDP (30 mg/kg) failed to disrupt percent correct performance on the tasks although response latencies showed an increase, leading in some cases to a failure to respond within the allocated time.

Animals↗
PubMed1979

Effects of sodium amylobarbitone on memory processes in the pigeon.

An experiment was carried out in the pigeon to assess the effects of sodium amylobarbitone (SAB) on memory, using a delayed pair comparison task. Performance was disrupted at all delays by doses of 10 and 20 mg/kg SAB and it was concluded that this effect was not due to perceptual impairment or stereotyped responding, which the drug might have caused, since performance on a visual discrimination task was unaffected by the same doses of SAB. Two further experiments assessed proactive and retroactive effects by varying the inter-trial interval and by introducing an irrelevant orange stimulus at various stages of the delay interval. Although these manipulations disrupted performance, there was no evidence to suggest that the drug potentiated their effects in a specific manner. The results are discussed in terms of an encoding hypothesis, and some reference is made to the possible neuropharmacological basis of action of this drug.

Amobarbital↗
PubMed1978

The effects of chlordiazepoxide on a delayed pair comparison task in pigeons.

Five pigeons were successfully taught a variation of the Konorski delayed pair comparison task, using a red and a green stimulus. The bird was required to respond to the left or right hand key, depending on whether the 2 successively presented centre key stimuli were the same (left) or different (right). The delay intervals ranged from zero to 9 s, and stable performance decrements (with increasing delay) were obtained. Chlordiazepoxide which, it has been argued, produces behavioural changes similar to those observed after hippocampal lesions was found to disrupt performance at doses greater than 4 mg/kg (i.m.). All delays (including zero) were affected. Some interpretations of this result in terms of encoding and attention are discussed, and some reference made to the possible neuropharmacological basis of this drug action.

Animals↗
PubMed1978

Categorization and retrieval after selective inferotemporal lesions in monkeys.

Two variations of a colour matching to sample task, with and without delay, were used to explore the deficits produced by bilateral foveal prestriate, posterior inferotemporal or anterior inferotemporal cortex lesions in monkeys. In the first task, 7 colours served as samples, but matching had to be done from only 4 alternative stimuli (7s x 4a); this task taxes the animal's ability to categorize information. In the second variation of matching to sample only 4 colours served as samples, but matching had to be done from amongst 8 alternative stimuli (4s x 8a); here, ability to retrieve information is tested. Task comparisons showed that the posterior inferotemporal group performed poorly on the 7s x 4a problem, whilst the AIT group were worse on the 4s x 8a task. It is concluded that posterior inferotemporal lesions disrupt categorization, whereas anterior inferotemporal lesions affect the retrieval of information.

Animals↗
PubMed1977

Benzodiazepines and discrimination behaviour: dissociation of response and sensory factors.

Ten London pigeons were trained on a schedule which allowed concurrent measurement of motor and exteroceptive sensory changes. The task involved a conditional colour discrimination contingent upon the completion of a fixed interval schedule of responding. As a preliminary pharmacological study the effects of the benzodiazepines, chlordiazepoxide and flurazepam were investigated. Both drugs enhanced perseverative responding (after completion of the FI), and to a variable degree responding during the FI, although there was no evidence for an increase in responding during the inter-trial-intervals. On the other hand, no marked changes in discrimination performance were observed. It is concluded that the most significant effects of these benzodiazepines are on motor mechanisms.

Animals↗
PubMed1975

Colour preferences in the pigeon: a behavioural and psychopharmacological study.

Ten London pigeons were tested in an operant apparatus, and found to have marked colour preferences, blue being preferred over green, followed by yellow and red. The effects of 2 tranquilizers, diazepam and chlorpromazine, were studied and it was found that diazepam released responding, and chlorpromazine suppressed it. Diazepam also tended to abolish colour preference, whilst chlorpromazine was effective only at the highest dose used (5.00 mg/kg). The implications of these findings, particularly in relation to the design of experiments and to the aversiveness of certain stimuli, are discussed.

Animals↗
PubMed1975

Response preferences of monkeys (Macaca mulatta) within wavelength and line-tilt dimensions.

Four rhesus monkeys were tested for preferences within the wavelength and line-tilt dimensions. In the case of wavelength, the response panel was back-illuminated by light of one of the following wavelengths, presented in a random manner: 470, 525, 580, and 635 nm. Similarly, the line-tilt dimension was studied, by presenting a 5 cm by 0.3 cm black bar tilted at 0, 30, 60, or 90 degrees. No preferences were found within this latter dimension; in contrast, marked wavelength preferences existed, the order of preference being 470 (most preferred), 525, 580, and 635 nm (least preferred). These response preferences were resistant to behavioral manipulation; the number of responses to blue and to red in extinction was about equal when red was used as the training stimulus, but vastly different following training on blue. These results indicate that such response preferences must be taken into account in the design of a wide variety of experiments.

Journal Article↗
PubMedDate not supplied

Simple standardised neuropsychological assessments aid in the differential diagnosis of dementia with Lewy bodies from Alzheimer's disease and vascular dementia.

Consecutive patients from a dementia case register received a standardised evaluation which incorporated a neuropsychological assessment with the Cambridge Assessment for disorders in the elderly (CAMCOG). Operationalised clinical diagnoses were made (consensus criteria for dementia with Lewy bodies, DLB; NINCDS- ADRDA for Alzheimer's disease, AD, NINCDS AIRENS for vascular dementia, VaD). Two-hundred and twenty-eight patients were studied (DLB 54, AD102, VaD 72). DLB patients had significantly better performance on recent memory than AD patients, but more impaired visuospatial praxis. DLB patients also had significantly better recent memory than those with VaD. Optimal cut-off points for the recent memory:praxis ratio achieved good discrimination between DLB and both other dementias.

Aged↗