By utilizing new information from both clinical and experimental (lesion, electrophysiological, and gene-activation) studies with animals, the anatomy underlying anterograde amnesia has been reformulated. The distinction between temporal lobe and diencephalic amnesia is of limited value in that a common feature of anterograde amnesia is damage to part of an “extended hippocampal system” comprising the hippocampus, the fornix, the mamillary bodies, and the anterior thalamic nuclei. This view, which can be traced back to Delay and Brion (1969), differs from other recent models in placing critical importance on the efferents from the hippocampus via the fornix to the diencephalon. These are necessary for the encoding and, hence, the effective subsequent recall of episodic memory. An additional feature of this hippocampal–anterior thalamic axis is the presence of projections back from the diencephalon to the temporal cortex and hippocampus that also support episodic memory. In contrast, this hippocampal system is not required for tests of item recognition that primarily tax familiarity judgements. Familiarity judgements reflect an independent process that depends on a distinct system involving the perirhinal cortex of the temporal lobe and the medial dorsal nucleus of the thalamus. In the large majority of amnesic cases both the hippocampal–anterior thalamic and the perirhinal–medial dorsal thalamic systems are compromised, leading to severe deficits in both recall and recognition.

/pdf/episodic-memory-amnesia-and-the-hippocampal-anterior-50qwk8ap9b.pdf

Episodic memory, amnesia, and the hippocampal–anterior thalamic axis.

The mechanisms involved in plasticity in the nervous system are thought to support cognition, and some of these processes are affected during normal ageing. Notably, cognitive functions that rely on the medial temporal lobe and prefrontal cortex, such as learning, memory and executive function, show considerable age-related decline. It is therefore not surprising that several neural mechanisms in these brain areas also seem to be particularly vulnerable during the ageing process. In this review, we discuss major advances in our understanding of age-related changes in the medial temporal lobe and prefrontal cortex and how these changes in functional plasticity contribute to behavioural impairments in the absence of significant pathology.

Neural plasticity in the ageing brain

Socioeconomic status (SES) is associated with childhood cognitive achievement. In previous research we found that this association shows neural specificity; specifically we found that groups of low and middle SES children differed disproportionately in perisylvian/language and prefrontal/executive abilities relative to other neurocognitive abilities. Here we address several new questions: To what extent does this disparity between groups reflect a gradient of SES-related individual differences in neurocognitive development, as opposed to a more categorical difference? What other neurocognitive systems differ across individuals as a function of SES? Does linguistic ability mediate SES differences in other systems? And how do specific prefrontal/executive subsystems vary with SES? One hundred and fifty healthy, socioeconomically diverse first-graders were administered tasks tapping language, visuospatial skills, memory, working memory, cognitive control, and reward processing. SES explained over 30% of the variance in language, and a smaller but highly significant portion of the variance in most other systems. Statistically mediating factors and possible interventional approaches are discussed.

/pdf/socioeconomic-gradients-predict-individual-differences-in-4xeqvlkemd.pdf

Socioeconomic Gradients Predict Individual Differences in Neurocognitive Abilities.

Causal Models of Attention-Deficit/Hyperactivity Disorder: From Common Simple Deficits to Multiple Developmental Pathways

Essential Role for TrkB Receptors in Hippocampus-Mediated Learning

Lesions of the intralaminar thalamic nuclei (ILn), the medial wall (MW) area of prefrontal cortex, and the hippocampus were compared and found to have distinct effects on delayed matching-to-sample (DMS) and delayed non-matching-to-sample (DNMS) tasks based on different types of stimulus cues. Hippocampal lesions impaired DNMS trained in a radial arm maze but had little effect on DMS trained with retractable levers or olfactory DNMS. MW lesions affected the DMS task but had limited effects on olfactory DNMS and radial arm maze DNMS. ILn lesions resulted in a more generalized pattern of impairment for radial maze tasks and (in previous studies) for the DMS and olfactory DNMS tasks. Only the hippocampal lesion was associated with a delay-dependent impairment. It is argued that ILn lesions disrupt remembering through their effects on the recurrent, feedback pathways that link functionally related areas of the basal ganglia and cortex.

Lesions of the frontal cortex, hippocampus, and intralaminar thalamic nuclei have distinct effects on remembering in rats

We conducted 2 studies to determine the importance of several brain systems for remembering odorants in a go/no-go delayed nonmatching-to-sample (DNMTS) task. In Experiment 1, impairments were observed for lesions of pyriform cortex or (to a lesser extent) the lateral internal medullary lamina of thalamus. Lesions of the entorhinal cortex or the mediodorsal (MDn) or the paracentral and centrolateral (PC-CL) thalamic nuclei did not affect DNMTS. In Experiment 2, an impairment comparable to the pyriform lesion was observed for a lesion of the intralaminar nuclei (PC-CL plus the central medial nucleus) but not for a larger lesion of MDn. None of the lesions in either study affected the ability to learn a 2-choice odor discrimination using go/no-go procedures comparable with the DNMTS task.

Effects of thalamic and olfactory cortical lesions on continuous olfactory delayed nonmatching-to-sample and olfactory discrimination in rats (Rattus norvegicus)

A comparison of the effects of hippocampal or prefrontal cortical lesions on three versions of delayed non-matching-to-sample based on positional or spatial cues.

http://jabur2.people.wm.edu/bbr_burk_and_mair_v123.pdf

Effects of intralaminar thalamic lesions on sensory attention and motor intention in the rat: a comparison with lesions involving frontal cortex and hippocampus.

Lesions involving the intralaminar thalamic nuclei have been associated with impairments in working memory and intentional motor function in human clinical cases and animal models of amnesia. The intralaminar nuclei have afferent and efferent connections related to striatum. To test whether disruption of striatal function can account for impairments produced by intralaminar lesions, we investigated the effects of striatal lesions on two tasks known to be impaired by intralaminar damage in the rat: radial maze delayed nonmatching (DNM), a measure of spatial working memory, and self-paced serial reaction time (SRT), a measure of intentional response speed. We compared the effects of lesions in four sites: the medial and lateral caudate putamen, nucleus accumbens, and olfactory tubercle. We found that lesions of the medial, accumbens, or tubercle sites impaired DNM performance, and that lesions of the lateral caudate putamen increased choice response time for the SRT task. There was a double dissociation between the effects of the ventral and the lateral lesions on these two tasks. For both tasks, the effects of striatal lesions were qualitatively similar and at least as large as intralaminar lesions in previous studies. These results provide evidence that striatal dysfunction can account for the DNM and SRT impairments produced by intralaminar lesions. The dissociation of functional impairments suggests that lateral sensorimotor areas of caudate putamen are important for responding based on external sensory stimuli and limbic-related areas in ventral striatum are important for responding based on information held in working memory.

https://www.jneurosci.org/content/jneuro/22/15/6756.full.pdf

Joshua A. Burk

Papers

Lesions of the frontal cortex, hippocampus, and intralaminar thalamic nuclei have distinct effects on remembering in rats

Effects of thalamic and olfactory cortical lesions on continuous olfactory delayed nonmatching-to-sample and olfactory discrimination in rats (Rattus norvegicus)

A comparison of the effects of hippocampal or prefrontal cortical lesions on three versions of delayed non-matching-to-sample based on positional or spatial cues.

Effects of intralaminar thalamic lesions on sensory attention and motor intention in the rat: a comparison with lesions involving frontal cortex and hippocampus.

A double dissociation within striatum between serial reaction time and radial maze delayed nonmatching performance in rats.