A substantial body of previous research suggests that the medial prefrontal cortex (MPFC) plays an important role in multiple aspects of emotion. These aspects include, but are not limited to, (1) generating, (2) experiencing, and (3) regulating one's own emotional state, as well as (4) facilitating the use of emotion-related information within goal-directed cognition and action selection. However, there is considerable controversy with regard to the distinct functional roles of various MPFC subregions. In this dissertation, I first provide a review of the theoretical and experimental literature to date in order to defend a plausible model of the hierarchical neural processes associated with each of the aspects of emotion highlighted above. This model proposes that different MPFC subregions each play distinct, but interactive, roles at or near the top of the respective hierarchical systems associated with those aspects of emotion. After reviewing this model, I then provide a description of four experiments that test the predictions of this model's claims regarding the roles of three distinct MPFC subregions: the rostral anterior cingulate cortex (rACC), the dorsomedial prefrontal cortex (DMPFC), and the ventromedial prefrontal cortex (VMPFC). These experiments provide independent support for the claims that (1) rACC plays an important role in representing the conceptual meaning of one's felt emotional reactions, (2) DMPFC plays an important role in maintaining representations of one's own emotions within a consciously accessible state, and (3) VMPFC plays an important role in both appraising the emotional significance of one's current situation and triggering the somatic/visceral reactions associated with the generation of an emotional response. In the concluding section of the dissertation, I then integrate these findings together with the larger model and discuss important directions for future research as well as ways in which the model might be extended to include insights from recent advances in theoretical neuroscience associated with predictive coding.

This dissertation investigated different factors contributing to age differences in working memory (WM) performance. Younger and older adults participated in five experiments, four on visuospatial WM (VSWM) and one on verbal WM. All addressed methodological issues that may differentially lower older adults’ performance. Experiments 1a and 1b manipulated the administration of a VSWM span task, with participants performing the task under either an ascending format (shortest sets presented first), or an interference-reducing descending format (longest sets presented first). Older adults’ performed significantly better in the descending compared to ascending format, consistent with an age-related susceptibility to proactive interference (PI). By contrast, younger adults did better in the ascending compared to descending condition, possibly due to their ability to benefit from practice and strategy use when easier trials are presented first. Experiment 2 considered how the similarity of task material influenced the build-up of PI and whether or not the combination of two PI-reducing manipulations (i.e., descending format and distinct trials) would further improve older adults’ performance. Distinctiveness helped older adults on the ascending format; however, combining distinct trials and a descending format provided no additional benefit. Experiment 3 considered whether or not synchronizing a VSWM task with an individual’s circadian arousal pattern would moderate interference effects, with the task administered at a peak or off-peak time of day. Peak-time administration improved older adults’ performance on the descending, but not the ascending, condition. Experiment 4 investigated the possibility that the serial order requirement of many WM tasks contributes to age differences in performance. Younger and older adults participated in a verbal WM span task – Operation Span - under either serial order or free recall instructions. Typical age differences were found when order but not free recall was required. Further analyses of the order condition data revealed that older adults were, in fact, recalling the items just as well as young adults, only not in the correct order. Taken together, the findings strongly suggest that age differences found on typical WM span tasks are influenced by numerous factors, such as task presentation, individual circadian arousal patterns, material similarity, and recall instructions.

Math difficulties (MD) are nearly as common as difficulties with reading. Despite this, MDs have received much less attention from researchers and we have yet to define a core cognitive process for MD. Knowledge about a core cognitive process would assist with early identification and remediation of MDs. Working memory has been identified as one cognitive process that is strongly associated with math difficulties. Most research examining the association between working memory and math calculation skills has been predicated on Baddeley and Hitch’s (1974) multicomponent model of working memory. Results of studies are inconclusive with respect to which component of Baddeley and Hitch’s model is most associated with math calculation skills. The wide variety of tasks that have been used to measure the components of Baddeley and Hitch’s model may be one reason for the lack of consistent findings. In the Introduction, common tasks used to measure the components of Baddeley and Hitch’s model are described and discussed. The Automated Working Memory Assessment Battery (AWMA) is suggested as a measure that adequately assesses all components of Baddeley and Hitch’s model. The AWMA was used in two studies examining the role of the components of working memory in math calculation skill in elementary-school (Study 1) and university (Study 2) students. Participants in Study 1were 94 (42 female) elementary-school children (M age = 9 years 1 month; Range 6 years 0 months – 11 years 8 months). Participants in Study 2 were 42 university students (M age 20 years 9 months; Range 18 years 6 months to 22 years 11 months). In both studies, the visuospatial sketchpad (short-term visuospatial memory) emerged as the component of working memory that explained the most variance in math calculation scores. In elementary-school children, phonological processing was also important. Evidence points to a developmental path emphasizing both verbal and visuospatial skills in math calculation skills of younger children and a more specific role for visuospatial memory in adults (university students). Explicit instruction using visuospatial strategies in the teaching of math calculation skills will be important at all ages.

Using an operant-olfactometer, the long term learning and memory, executive function, olfactory sensitivity, and working memory of the 5XFAD mouse model of Alzheimer’s disease was assessed. Six month old male and female 5XFAD and wildtype mice were tested. No deficits were found on an olfactory discrimination task or a reversal learning task. Female and transgenic mice performed better than male and wildtype mice on the higher odour concentrations, but not the lower concentrations, of the sensitivity task, suggesting differences in learning rate or maximum performance on the task, but not olfactory detection. This study demonstrated for the first time that mice are able to learn an olfactory delayed matching to sample task with delays up to 30 seconds long. Female mice showed higher levels of performance on the matching to sample task than male mice, indicative of better working memory.

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Objective: The purpose of this study was to investigate the impact of salience on the comprehension of predictive inferences in adults with traumatic brain injury (TBI), by increasing the visual salience of the predictive sentence. This study also investigated whether a relationship existed between performance on a predictive inferencing comprehension task and working memory for this population. Increasing the salience of a crucial sentence in the predictive inferencing task may lead to better memory for the inferred information within the focused portion of the text (Gernsbacher & Jescheniak, 1995; Parkhurst, Law, & Niebur, 2002). Method: Six participants with TBI and six non-brain injured peers (NBI) took part in the study. Each participant was administered an inference comprehension task which consisted of a series of 55 stories. Each story incorporated one of five conditions: 1) a Recent salient condition (inferred information immediately preceded the comprehension question and was visually salient); 2) a Recent non-salient condition (inferred information immediately preceded the comprehension question but was not visually salient); 3) a Distant salient condition (inferred information occurred early in the story and was visually salient); 4) a Distant non-salient condition (inferred information occurred early in the story and was not visually salient); and 5) a Control condition (no inferred information in the story). In addition there were 20 filler stories. The predictive sentence was bolded in half the stories in order to increase the visual salience of the stimuli. In addition, a measure of working memory span (Lehman-Blake & Tompkins, 2001) was administered. Results: A significant main effect was found for Group, F(1,11) = 7.6, p= 0.019, with adults with TBI performing more poorly than matched controls. A significant main effect was also found for Condition, F(3,33) = 3.159, p = 0.038, with all participants performing more poorly in the Distant non-salient condition. No statistically significant interaction between Group x Condition was observed, F(3,33) = 0.469, p =0.706. Post-hoc comparisons revealed that all participants performed more poorly in the non-salient condition when the storage load was high (distant non-salient condition). Significant correlations were found for working memory span and the Distant salient condition (r =0.677, p < 0.05) and Distant non-salient condition (r = 0.646, p < 0.05). Conclusion: The results have both theoretical and clinical implications. Theoretically, the role of attention in working memory is of interest in language comprehension (e.g. Montgomery, Evans, & Gillam, 2009). This study may further contribute to studies of allocation of attention using increased salience to enhance comprehension. Clinically, the use of enhancing the salience of key information is a practical strategy that can be employed.

In humans, damage to the mammillothalamic tract (MTT) as a result of localised strokes, tumours or alcohol abuse has consistently been implicated in the severe anterograde amnesia evident in these patients. This small neural pathway, which connects the mammillary bodies (MB) to the anterior thalamic nuclei (ATN), is thought to provide one important link in a larger extended hippocampal circuit involved in encoding and retrieval of episodic memory. Brain damage in clinical cases is, however, typically diffuse and contributions from additional sites of pathology cannot be ruled out. There are also inconsistencies within a limited animal literature on MTT lesions. The current study made MTT lesions in female rats and used multiple „episodic - like‟ memory tasks relevant to the proposed importance of this pathway. The project also intended to test whether enrichment reduces any impairments after MTT lesions. None of the lesions resulted in complete bilateral disconnection of the MTT, but many had moderate to large bilateral (n = 6) (81% to 50%), or unilateral MTT damage (n = 4). Rats with bilateral lesions were compared to controls (n = 14, including 4 other lesion rats in which no lesion occurred). The severe working memory deficit in the water maze expected for rats with MTT lesion was not found and only a slight deficit in reference memory in the water maze was observed (so enrichment was not implemented). Although none of the bilateral MTT lesions were complete, they are also often incomplete in clinical cases and previous research has shown that lesions to the ATN in excess of 50% are sufficient to induce severe behavioural deficits in rats. Therefore, if the MTT is critical to memory then substantial but not total bilateral disconnection should be sufficient to induce profound deficits in rats, at least on spatial working memory. Taken together these findings suggest a less crucial role for the MTT in memory than previously suggested. Future research needs to resolve the inconsistencies observed in the animal literature by repeating the present study, using larger MTT lesions and both male and female rats.

This research explored whether variation in working memory ability helps account for the wide variation in toddlers' language skills and improves predictive models of language outcomes over time. A cohort of typically developing (TD) (n = 55) and late talking children (n = 24) were assessed at two time points. The initial assessment took place at ages 24-30 months and the outcome assessment occurred 18 months later, when the children were aged 41-49 months. The assessment battery included standardised tests of language and visual cognition; assessments representing aspects of Baddeley's model of working memory: phonological short term memory (PSTM), a measure of processing speed, verbal working memory (VWM), visual spatial working memory (VSWM), and a parent report questionnaire of executive functioning (EF). Study 1 explored the associations between these aspects of working memory and concurrent expressive vocabulary at ages 24-30 months and examined group differences in the measures between TD and late talking children. Study 2 explored associations between aspects of working memory and concurrent expressive language in the same cohort at 41-49 months of age. Group differences in the measures between resolved late talkers (RLTs) and TD children were explored. Finally Study 3 explored the ability of the measures used at 24-30 months to predict language outcomes at 41-49 months. These results were considered in relation to the prediction of language outcomes on group and individual levels. Overall the results indicated a strong relationship between early PSTM and early language measures. A novel finding was that PSTM was significantly lower in the late talking and RLT groups compared with the TD groups, even after controlling for group differences in language and phonology at both time points. This confirms previous research that PSTM plays a role in early expressive vocabulary acquisition, and suggests that early PSTM deficits may be a causal factor for some cases of late talking. For the whole group, three working memory variables (VWM, Emotional Control and Shift) measured at 24-30 months added unique variance to predictive models in total language scores at 41-49 months after previously established early predictors (receptive language and parent education) had been entered into the hierarchical regression model (receptive language R²Δ = 59%; parent education R²Δ = 2%; VWM R²Δ = 8%; Emotional Control R²Δ = 1% and Shift R²Δ = 2%). This is another novel finding which supports the concept of working memory playing a unique role in language acquisition between the ages two and four years. Processing speed did not contribute unique variance to regression models predicting language when other working memory measures were included. The A not B task (measuring VSWM) did not correlate with language. There were concerns with construct validity with the EF parent report measure (Behaviour Rating Inventory of Executive Function – Preschool Version), which meant that the results from this assessment were interpreted with caution. In terms of clinical outcomes, 83% of the late talkers resolved their language delays over the 18 month period, but as a group showed a seven-fold increase in being identified for clinical concerns at the outcome assessment than children who were not late talkers. The majority of these concerns were for poor phonology. While early VWM, Shift and Emotional Control added unique variance to outcome total language scores on a group level, they did not improve prediction of individual outcomes in language impairment status at 41-49 months. Early receptive language delay was a more powerful predictor of later language impairment than late talking in this cohort, as these children (n = 9) showed only a 44% rate of resolution.

The interaction between exercise and cognitive task performance has been previously examined using cycle ergometer and treadmill running tasks. The interaction between natural (non-constrained) exercise and cognitive task performance has, however, been well less examined. An example of a natural exercise task would be running outdoors on a steep trail where route selection and foot placement are critical for the runner. The performance of runners is examined in a dual trail-running and working memory task. The working memory task involved counting tones, and was performed at both a low workload, in which they were asked to count every fourth low frequency tone and a high workload in which they were asked to count every fourth low, medium and high frequency tone. In experiment 1, runners performed the tone-counting tasks both while running on a steep trail with uneven terrain and while seated (control conditions). In addition, they ran the trail without a cognitive task load. Running distance and counting accuracy significantly decreased during the dual task trials, there was a linear trend the run distance decreased as the task got harder. As the secondary cognitive task demand increased running performance decreased (linear trend). Cognitive performance was only significantly impaired while running for the hard cognitive task (for the easy cognitive task there was no statistically significant difference). Participants reported an increased workload in the dual run-counting task conditions when compared with the seated task conditions. Reports of task focus and feeling of being spent (exhausted) also varied across task conditions. In experiment 2 unconstrained running was conducted in the same manner, on a flat-even terrain track to establish if the route selection and scanning required to negotiate uneven terrain was causing the dual-task interference, or if there is a general interference effect caused by the self-regulatory demands of running, or the direct demands of running itself (exercise). The linear trend of decreased running performance with increased secondary cognitive demand was similar to experiment 1 - the more cognitive load the less distance traveled. The effect on the cognitive task was, however, not evident in experiment 2; there was no statistically significant difference between cognitive task performance in the dual and single-task conditions. The findings outlined in these experiments, demonstrate dual cognitive tasks have a negative effect on running performance, and the cognitive task may also be affected depending on running intensity, particularly where self-paced natural running over terrain is coupled with complex cognitive tasks.

Scores from high-stakes tests such as the Scholastic Aptitude Test (SAT) are commonly used as criteria for college admission decisions. So, it is of implied importance to identify factors that contribute to susceptibility to failure on these tests. One potential factor addressed in the current study was whether emotional cognitive load differentially impacts those with low working memory capacity or trait anxiety. Individual differences in subjective arousal were also tested as a mechanism contributing to this effect. In Experiment 1, a reading comprehension task revealed that type of cognitive load affected accuracy. In Experiment 2, state anxiety was induced using methods from previous research. The results revealed that, again, only type of cognitive load affected comprehension accuracy. Together, results suggest that arousal induced via disturbing words negatively influence reading performance regardless of superior working memory capacity. These findings are not based on cognitive load in general, but the semantic value of the words processed, in particular, that led to comprehension difficulty. Results are discussed in terms of theoretical and practical implications.