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The activity of neurons in the prefrontal cortex (PFC) may underlie working memory processes in the brain. Both the performance of working memory tasks and the activity of PFC neurons are modulated by dopamine. The goal of the present thesis was to gain insight into the neural basis of working memory by studying the PFC, and the DA system in the PFC, from both a behavioral and cellular perspective. The functional contribution of the PFC to working memory processes in the rat was assessed in Chapter 2 of the present thesis using memory-based foraging tasks on an 8-arm radial maze. The results of these studies indicated that lidocaine-induced inactivations of the PFC selectively disrupted the ability to use mnemonic information to guide foraging, but not the ability to acquire or retain such information. The ability to use mnemonic information to guide foraging was also disrupted by microinjection of a D1 but not D2 receptor antagonist into the PFC. Chapters 3-5 investigated how PFC neurons process synaptic inputs to their dendrites to produce spike output. The intrinsic membrane properties and synaptic responses at the soma and dendrites of deep layer PFC pyramidal neurons were recorded using sharp intracellular or whole-cell patch-clamp techniques in a brain-slice preparation. Different passive and active membrane properties of the soma and dendrites of PFC neurons were observed. The distal dendrites of PFC neurons responded most effectively to strong, highly coincident synaptic inputs. Ca²⁺currents near the soma both amplified the effects of these inputs and modulated the spike output pattern. Spike output at the soma was also controlled by the interplay of slowly-inactivating Na⁺ and K⁺ currents. Chapter 6 investigated the modulation of PFC neurons by DA. DA or a D1 but not D2 receptor agonist increased the evoked firing of PFC neurons via a D1- mediated modulation of slowly-inactivating Na⁺ and K⁺ currents. Concurrently, D1 receptor activation reduced burst firing in PFC neurons, due to a attenuation of Ca²⁺ currents. D1 receptor activation also increased both GABA[sub A] IPSPs and NMDA EPSPs. The final chapter of this thesis integrated these data into a cellular model of PFC function and its modulation by DA. It is proposed that DA may tune PFC neurons such that they respond selectively to strong synchronized inputs from other cortical areas. In the presence of DA, working memory processes mediated by the PFC may be influenced selectively by stimuli of behavioral significance.

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In an immediate serial recall task, participants are asked to recall lists of items in order. In the Hebb repeating-list variant of the task, subjects are read a series of lists, and every third list is repeated. Performance improves across repetitions but is stable for the non-repeated trials. The repetition advantage—the increased accuracy for the repeated list—is known as the Hebb effect. Several models have been advanced to explain how participants order successive items, but how participants take advantage of the repetition has largely been ignored. Although the task is usually discussed in terms of recall of verbal items, the Hebb effect has been observed with sequences of visuo-spatial positions. The present work assesses whether immediate serial recall of verbal material benefits from visuo-spatial context. Sequences of letters were presented in different spatial positions in a visual version of the Hebb task. Presenting lists in random spatial positions on the periphery of an imaginary circle did not boost performance, but if the sequence was predictable, overall accuracy increased. The spatial path of successive items influenced the Hebb effect. When the distance between successive positions was minimized, participants were able to exploit the repetition early in practice. The results deny an account based on item distinctiveness. I discuss the results in terms of contemporary models of ISR. / Thesis (Master, Psychology) -- Queen's University, 2007-10-03 13:01:00.716

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The purpose of this study was to determine the effects of auditory background interference on test performance on a group of schizophrenics as well as with a normal group and to ascertain if subgroups of each type could be differentiated on neuopsychological measures from the WMS-R particularly sensitive to left-hemispheric functions.There were 60 subjects, 30 normals and 30 schizophrenics, who volunteered to participate in the study. The schizophrenics, all hospitalized at Logansport State Hospital, had a diagnosis of chronic undifferentiated schizophrenia. The normals were students at Logansport High School enrolled in a senior psychology class. The research utilized a counterbalanced design in which subjects were administered items from the Wechsler Memory Scale-Revised in both a normal administration condition and in the presence of auditory background information provided by a prerecorded tape.The relationship between auditory background interference and diagnosis was examined using an analysis of variance (MANOVA) of the difference between means. The overall mean for groups did not differ significantly, F (1,58) = .087. No test was identified as being able to differentiate left-hemispheric functions for either group in either testing condition, F (4, 55) = 1.09, p .37. There also was no statistically significant difference between the test performance of males and females in the presence of auditory background interference.The results indicate that neither group evidenced much change in perfromance in the presence of auditory background information. This would suggest that the testing conditionn had little influence on test results. It also suggests that internal differences, as opposed to the external environment, contributed much more to the differences in test performance. The lack of significant differences on the subtests that are considered measures of left-hemispheric functioning may have been due to the significant cognitive impairments of the schizophrenics. The normals may have been more able to increase their attentional and concentration skills in the presence of auditory background interference so that no decreases in performance resulted. / School of Physical Education

The major purpose of this study was to determine the effect of two mediational strategies, labeling and rehearsal, on the short-term memory of prelingual deaf children. The research question answered by this investigation examined whether inducing the use of a mediator was affected by age and the serial position of stimulus items presented.The population of prelingual, severely and profoundly deaf children of normal intelligence were screened for overt production of existing mediational techniques. Thirty-three nonproducing subjects were randomly assigned to three treatment groups at four age levels. Two groups were taught memory strategies, and the third group acted as a control. A single null hypothesis was tested using a 3x4x4 analysis of variance with repeated measures on the last factor. The .05 level of significance was predetermined as the critical probability level for rejecting the hypothesis.FINDINGS1. Differences in recall performance of prelingual deaf children who (a) were induced to label, (b) were induced to cumulatively rehearse, and (c) had no induced strategy did not vary as a function of age and serial position.2. Deaf children's performance on short-term, visual sequential memory tasks is a function of the type of preferred memory strategy and age.3. No differences in performance at the serial positions occurred as a function of age.4. The type of memory strategy used by prelingual deaf children did not result in differences in performance as a function of serial position.5. The youngest deaf children who rehearsed and labeled enhanced recall significantly better than those children who were taught no strategy.6. Most older subjects taught to rehearse recalled significantly better than the children taught to label and those who were not taught a memory technique.7. Late intermediate deaf children who rehearsed recalled better than those children taught to label, but not significantly different from those taught no strategy.8. The relationship among serial position levels showed primacy and recency effects on the memory curve.CONCLUSIONS1. The cognitive processes used by deaf children are similar to those used by hearing children.2. Cognitive processes used by deaf children are utilized for similar purposes as those used by hearing children.3. Deaf children appear to display a production deficiency with regard to the use of mediational strategies. / Department of Special Education