Biomedical subjects

M J Eacott

Publications and source records attributed to M J Eacott.

15 recordsLinked to original sources

PubMed1999

Childhood amnesia: on answering questions about very early life events.

Twenty five young adults were asked about the events surrounding the birth of a younger sibling which took place when they were under the age of 2 years. Approximately 40% of the participants claimed to have significant memories of the events. The mothers of our participants verified that a majority of their answers were accurate. Comparing the pattern of data with those previously collected (Eacott & Crawley, 1998) suggests that the memories of those who were aged below 2:0 are qualitatively similar to the memories of those who were older at the time of events and dissimilar in type to those who are basing their reports on reconstructions from family knowledge. This finding may be evidence that memories of events that occurred before the age of 2 years are genuine but rare. This conclusion may be useful in assessing theories of childhood amnesia.

Adult↗

PubMed1998

The offset of childhood amnesia: memory for events that occurred before age 3.

Adult memory for the events surrounding the birth of a sibling was examined in 69 adults. The authors identified a steep offset for childhood amnesia for this event before the child reaches age 2 1/2 years. The authors also examined the accuracy of information recalled. Although the majority of the answers were accurate, false memories were a consistent feature of the data. Alternative explanations of the authors' data were considered by examining the amount of information an additional 57 adults had about a family birth for which they could have no memory. The pattern of results did not support the view that participants might be unable to differentiate between memories and knowledge about the event.

Adult↗

PubMed1997

Ventral prefrontal cortex is not essential for working memory.

It is widely held that the prefrontal cortex is important for working memory. It has been suggested that the inferior convexity (IC) may play a special role in working memory for form and color (). We have therefore assessed the ability of monkeys with IC lesions to perform visual pattern association tasks and color-matching tasks, both with and without delay. In experiment 1, six monkeys were trained on a visual association task with delays of up to 2 sec. Conservative IC lesions that removed lateral area 47/12 in three animals had no effect on the task. Further experiments showed that these lesions had no effect on the postoperative new learning of a color-matching task with delays of up to 2 sec or versions of the visual association task involving delays of up to 8 sec. In experiment 2, larger lesions of both areas 47/12 and 45A were made in the three control animals. This lesion caused a profound deficit in the ability to relearn simultaneous color matching, but subsequent matching with delays of up to 8 sec was clearly unimpaired. We suggest that the IC may be more important for stimulus selection and attention as opposed to working memory.

Animals↗

PubMed1997

Spatial memory impairment in rats with fornix transection is not accompanied by a simple encoding deficit for directions of objects in visual space.

In Experiment 1, rats learned 6 discriminations among pairs of complex wide-angle visual displays, presented concurrently, using a computer-controlled Y maze. Fornix-transected rats were unimpaired relative to controls regardless of whether the displays comprised a single large "objectlike" figure or "scenelike" arrays of spatially distributed figures. Experiment 2 compared 2 versions of a visual discrimination in which either object identity (independent of location within the visual field) or location within the visual field (independent of object identity) had to be used. The fornix-transected rats performed normally with either cue. In Experiment 3, however, the same group was clearly impaired on a standard spatial memory test, spatial delayed nonmatching to sample. Although the fornix-transected rats were more likely to choose rapidly and inaccurately, their deficit was not a by-product of impulsive responding. The spatial impairment was not merely a difficulty in encoding direction of a single item within visual space, but more complex configural deficits could not be ruled out.

Animals↗

PubMed1997

The recognition memory deficit caused by mediodorsal thalamic lesion in non-human primates: a comparison with rhinal cortex lesion.

Two earlier studies found that rhinal cortex ablations in the monkey (Macaca fascicularis) impaired delayed matching-to-sample (DMS) when the stimuli in the experiment came from a large population of possible stimuli, but not when the stimulus population was small, while uncinate fascicle section had no effect on DMS whatever the stimulus population size. The mediodorsal thalamus receives a large projection from the rhinal cortex, and has been implicated in recognition memory performance. We trained monkeys preoperatively in delayed matching-to-sample with large and small stimulus populations, exactly as in the earlier studies, then examined the effect of bilaterally ablating the medial portion of the mediodorsal thalamic nucleus. Mediodorsal lesion impaired postoperative delayed matching-to-sample performance with a large stimulus set, but had no effect on performance of DMS with a small stimulus population. In comparison with the earlier data from rhinal cortex lesions with the same methods, wherever a deficit was seen in the rhinal-lesioned animals the mediodorsal thalamic nucleus-lesioned animals showed a smaller deficit. We conclude that other efferents from the rhinal cortex, possibly those to the adjacent inferior temporal cortex, enable better performance in the mediodorsal thalamic nucleus-lesioned animals than in the animals with rhinal cortex ablation.

Animals↗

PubMed1995

Visual learning for an auditory secondary reinforcer by macaques is intact after uncinate fascicle section: indirect evidence for the involvement of the corpus striatum.

Three cynomolgus monkeys (Macaca fascicularis) were trained preoperatively in visual discrimination learning for an auditory secondary reinforcer. Each new discrimination problem was solved on the basis of the secondary reinforcer, and primary reinforcement (food reward) was given only after a new problem had been solved. The animals learned 50 new problems in each daily session and it was therefore possible to assess accurately their average rate of learning new discrimination problems in this procedure. After the learning rate had stabilized preoperatively the animals were operated upon to transect the uncinate fascicle, the cortico-cortical pathway from visual association cortex in the temporal lobe to prefrontal cortex. The animals' learning rate was unchanged after uncinate fascicle section. A previous experiment has shown that visual learning for an auditory secondary reinforcer is unaffected by disconnection of visual association cortex from the amygdala and the fornix. Taken together, this negative evidence points strongly to the conclusion that visual learning for an auditory secondary reinforcer depends upon interaction of temporal lobe visual association cortex with the corpus striatum, since other possibilities have been excluded.

Acoustic Stimulation↗

PubMed1995

Uncinate fascicle section leaves delayed matching-to-sample intact, with both large and small stimulus sets.

An earlier study found that rhinal cortex ablations in the monkey (Macaca fascicularis) impaired delayed matching-to-sample only when the stimuli in the experiment came from a large population of possible stimuli, not when the stimulus population was small. The present experiment tested the idea that delayed matching-to-sample with a small stimulus population selectively engages the direct projection from visual association cortex to the prefrontal cortex, bypassing the rhinal cortex. This selective involvement could explain the preservation, after rhinal cortex ablations, of memory for items drawn from a small stimulus population. We trained monkeys preoperatively in delayed matching-to-sample with large and small stimulus populations, exactly as in the earlier study, then examined the effect of sectioning the cortico-cortical pathway between visual association cortex and prefrontal cortex, the uncinate fascicle. Uncinate fascicle section had no effect on postoperative performance of delayed matching-to-sample, with either large or small stimulus populations. These data give no support to the idea that preserved matching with a small stimulus population after rhinal lesions reflects the selective involvement in this task of the direct projection from visual association cortex to prefrontal cortex. Further, they strengthen the idea (derived from earlier studies of uncinate fascicle section) that the uncinate fascicle does not play a general role in visual memory or perception, but instead has a specialized function in the processing of conditional instruction cues.

Animals↗

PubMed1995

A computer-controlled maze environment for testing visual memory in the rat.

A computer-controlled version of a Y-maze was developed to allow automated testing of rats' learning and memory with visual stimuli. Each of the 3 arms terminated with 2 adjacent monochromatic screens, 43 cm from the maze centre, providing a total stimulus area 47 cm wide by 18.5 cm high. The displays were abstract patterns extending across 2 screens, generated by algorithms which provided a large pool of discriminable patterns. The patterns used were of 2 general classes: Scenes (internally complex patterns with varying numbers of foreground shapes distributed across contrasted backgrounds) and Objects (internally homogeneous single figures, confined to the central part of the display). They could be stationary or have oscillatory movement. Subjects' location in the maze was monitored by infrared beam photodetectors; approach to correct patterns was rewarded with food. Pigmented rats of the Hooded Lister and Dark Agouti strains were tested. All could acquire 2-pair concurrent visual discriminations comprising 2 positive and 2 negative patterns, either Scenes or Objects; most could acquire 4-pair discriminations. Dark Agouti rats generally performed better than Hooded Listers. A novel training procedure using one positive and many negative patterns resulted in rapid learning of novel discriminations with either moving or non-moving patterns. The apparatus is an effective environment for visual learning by rats, suitable for a wide range of tasks in neuropsychology and psychopharmacology.

Animals↗

PubMed1995

Perception and memory: action and interaction.

Receptive field properties of neurons in, and the effects of cortical ablation of, inferior regions of the macaque temporal lobe reveal their role in the visual representation of objects. However, changes in receptive field properties, as a result of visual experience with specific objects or patterns, suggest that cells encode both sensory and mnemonic features of a visual stimulus. Thus, in addition to selectivity for the visual qualities of a stimulus, response properties of cells indicate their involvement with mechanisms of visual associative and visual recognition memory. Recently, ablation studies have extended the putative role of these neurons in memory. These results suggest that the anterior inferotemporal cortex not only plays a role in recognition memory by signaling novelty or familiarity and in coding for visual associative memory but also modifies responses of neurons to the stimuli themselves, playing a part in the visual learning that underlies sensory classification of complex visual discriminanda.

Animals↗

PubMed1994

Preserved recognition memory for small sets, and impaired stimulus identification for large sets, following rhinal cortex ablations in monkeys.

Seven cynomolgus monkeys (Macaca fascicularis) performed a series of tasks designed to assess their visual memory and their ability to identify visual stimuli. Preoperatively they were trained and tested in delayed and simultaneous matching-to-sample, both with a large stimulus set and with a small stimulus set; there were approximately 500 million possible stimuli in the large set, which effectively means that stimuli were trial-unique with this set, while in the small set there were only four stimuli, which appeared repeatedly in every session of training with the small set. Three of the monkeys then had the cortex within and adjacent to the rhinal sulcus removed bilaterally, while the other four served as an unoperated control group. Postoperatively, the animals with ablation of the rhinal cortex showed severe impairment in delayed matching-to-sample with the large set. With the large set they were also impaired, however, in matching-to-sample with no delay between sample and test (0 s delay) and in simultaneous matching-to-sample, in which the sample and the two choice patterns were simultaneously present for inspection. The impairment in simultaneous matching-to-sample was particularly clear when the task was made more difficult by reducing the physical discriminability of the trial-unique stimuli. With the small set of four stimuli, the animals with rhinal cortex ablation were not significantly impaired in overall performance level in delayed matching-to-sample, though their level was on average below that of the normal control animals. The stimulus set was then further restricted, so that there were now only two stimuli used throughout; in this condition, the animals with rhinal cortex ablation performed delayed matching-to-sample without any suggestion of impairment, showing indistinguishable performance levels from those of the control animals over a range of forgetting intervals. Subsequently, the animals were trained in trial-unique non-matching-to-sample with 0 s delay, which required reversal of the matching-to-sample rule they had previously learned; animals with rhinal cortex ablation showed a clear impairment in this rule-reversal learning. The final experimental task was a concurrent discrimination learning task in which 20 pairs of stimuli were presented once per session; the animals with rhinal cortex ablation learned more slowly than the control animals on average, but the difference between the groups did not attain statistical significance.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Visual discrimination impairments following lesions of the superior temporal sulcus are not specific for facial stimuli.

Six rhesus monkeys took part in an experiment on visual learning. In three of the monkeys the part of the superior temporal sulcus in which many of the cells respond selectively to some aspect of faces was removed, while the remaining three animals served as unoperated controls. In Experiment 1 they learned a series of two-choice visual discriminations between patterns. The animals with lesions of the superior temporal sulcus were markedly impaired. The discriminations were of two types: in the first, the discriminanda differed in shape (e.g. Y and 3), while in the second they differed only in their orientation (e.g. ). Unlike animals with lesions to the neighbouring inferior temporal cortex who are impaired on shape but not orientation discriminations, animals with lesions of the superior temporal sulcus were equally impaired on both types of discrimination. In Experiment 2 the same six animals learned a series of discriminations between discriminanda which consisted of photographs of pairs of eyes. Each discrimination was between a set of eyes which looked directly at the viewer and a set in which the gaze was laterally averted to varying degrees. Again, animals with lesions of the superior temporal sulcus showed a marked impairment. We conclude that this impairment may be a general impairment in two-choice visual discrimination learning, rather than a selective impairment in discrimination of eye gaze. This result warns against a simple interpretation of the function of this area as a "face area", concerned only, or chiefly, with the perception and significance of parts of the body, notably faces, and their movements.

Animals↗

PubMed1991

The role of monkey inferior parietal cortex in visual discrimination of identity and orientation of shapes.

Three cynomolgus monkeys (Macaca fascicularis) were tested for their visual learning ability following bilateral lesions to the inferior parietal cortex. In discrimination learning with patterns differing from each other in form and colour their performance was normal. In discriminating monochromatic patterns their performance depended on the nature of the pattern discrimination; when the discriminanda were different shapes (e.g. x,v) they performed well, while with discriminanda which differed only in the orientation of the shape (e.g. p,d) they performed relatively badly. These results were compared to the previously reported results of normal animals and animals with inferior temporal lesions performing the same task. The ratio of errors in orientation discrimination to errors in shape discrimination was significantly higher than normal in the group with parietal lesions, and significantly lower than normal in the group with inferior temporal lesions. These results suggest that the roles of inferior temporal and inferior parietal cortex in the discrimination of shape and orientation are complementary.

Animals↗

PubMed1990

Interhemispheric transfer of visuomotor conditional learning via the anterior corpus callosum of monkeys.

Two experiments examined interhemispheric transfer of learning across the anterior corpus callosum in monkeys (Macaca fascicularis). The animals learned a series of visuomotor conditional discrimination problems for food reward. Within each problem the animals were first trained using one hand to make the motor responses, and were then required to use the opposite hand in order to test for intermanual transfer of the initial learning. In Exp. 1, a group of animals with surgical section of the entire corpus callosum and anterior commissure showed a complete absence of intermanual transfer of learning. A second group, in which only the anterior commissure and the posterior part of the corpus callosum were sectioned, leaving the anterior corpus callosum intact, showed good intermanual transfer. Thus, intermanual transfer in the second group represented interhemispheric information transfer via the anterior portions of the corpus callosum. However, in Expt. 2, normal intermanual transfer was seen in a group of animals in which the anterior corpus callosum alone had been sectioned. We conclude that the anterior corpus callosum can mediate interhemispheric transfer of visuomotor conditional learning, but is not the only available route for such transfer in the present task.

Animals↗

PubMed1989

Interhemispheric transfer of visual learning in monkeys with intact optic chiasm.

The purpose of the present experiments was to investigate the role of the forebrain commissures in interhemispheric visual transfer when both eyes are open and the optic chiasm is intact. Cynomolgus monkeys (Macaca fascicularis) learned a series of two-choice simultaneous visual discriminations. The visual stimuli were bipartite, with independently determined left and right halves. If such a stimulus is fixated centrally, the two halves fall into opposite visual hemifields. After 10 trials of acquisition of each discrimination, the same discriminanda were presented for a further 10 trials in which, within each stimulus, the positions of the halves were exchanged: the left half became the right and vice versa. The unoperated animals transferred well to the altered stimuli, making many fewer errors than they made in learning the originally presented discrimination. In contrast, monkeys with section of the posterior corpus callosum and the anterior commissure transferred poorly. These effects show that the forebrain commissures are important for the interhemispheric transfer and integration of visual information in animals with a normal, intact peripheral visual system.

Animals↗

PubMed1989

Reaching to a rewarded visual stimulus: interhemispheric conflict and hand use in monkeys with forebrain commissurotomy.

Monkeys (Macaca fascicularis) learned simultaneous visual discriminations for food reward. Two coloured patterns were presented one above the other and the monkey chose one by touching it with a hand. On some trials, conflicting information was presented to the two visual hemifields. For example, in the left hemifield the stimulus associated with reward was in the higher position and in the right hemifield the stimulus associated with reward was in the lower position. On some of these conflict trials the monkeys were required to use the left hand and on others the right. Normal monkeys, monkeys with section of the anterior commissure and the posterior corpus callosum, and monkeys with section of the anterior commissure and the whole of the corpus callosum performed this task. Our aim was to test the hypothesis that following forebrain commissurotomy, the response made by each hand would be predominantly influenced by the visual information put into the hemisphere contralateral to that hand. If this is true then choices in the conflict test should vary systematically with hand use. This hypothesis was not confirmed. We conclude that when a monkey reaches to a rewarded visual stimulus, information about the reward history of the stimulus is integrated between the hemispheres before influencing the motor control of the hand that reaches, either by a peripheral or a subcortical route.

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