Dementia associated with dorsal midbrain lesion

Diabetes and Cognitive Decline in Older Adults: The Ginkgo Evaluation of Memory Study

BACKGROUND

Previous studies have shown that individuals with diabetes exhibit accelerated cognitive decline. However, methodological limitations have limited the quality of this evidence. Heterogeneity in study design, cognitive test administration, and methods of analysis of cognitive data have made it difficult to synthesize and translate findings to practice. We analyzed longitudinal data from the Ginkgo Evaluation of Memory Study to test our hypothesis that older adults with diabetes have greater test-specific and domain-specific cognitive declines compared to older adults without diabetes.

METHODS

Tests of memory, visuo-spatial construction, language, psychomotor speed, and executive function were administered. Test scores were standardized to z-scores and averaged to yield domain scores. Linear random effects models were used to compare baseline differences and changes over time in test and domain scores among individuals with and without diabetes.

RESULTS

Among the 3,069 adults, aged 72-96 years, 9.3% reported diabetes. Over a median follow-up of 6.1 years, participants with diabetes exhibited greater baseline differences in a test of executive function (trail making test, Part B) and greater declines in a test of language (phonemic verbal fluency). For the composite cognitive domain scores, participants with diabetes exhibited lower baseline executive function and global cognition domain scores, but no significant differences in the rate of decline.

CONCLUSIONS

Identifying cognitive domains most affected by diabetes can lead to targeted risk modification, possibly in the form of lifestyle interventions such as diet and physical activity, which we know to be beneficial for improving vascular risk factors, such as diabetes, and therefore may reduce the risk of executive dysfunction and possible dementia.

The effects of a midbrain glioma on memory and other functions: a longitudinal single case study

Our understanding of the effects of midbrain damage on cognition is largely based on animal studies, though there have been occasional investigations of the effects of human midbrain lesions on cognition. This investigation of a rare case of a glioma initially confined to the dorsal midbrain explores the effects of disease progression on IQ, memory, and choice reaction time. Extensive dorsal midbrain damage did not appear to affect IQ and various memory functions (including span, working memory, story recall, and remote memory). Choice reaction time latencies increased, while verbal and spatial learning and long-term memory deteriorated with tumour growth, but it was not clear how far the deterioration reflected midbrain damage or damage outside the midbrain.

The neuro-behavioural syndrome of brainstem disease

We describe two patients with isolated brainstem lesions who exhibited behavioural and cognitive changes that are commonly associated with frontal lobe pathology, as leading clinical features. These cases illustrate the role of distributed neural networks in cognitive and behavioural processes. The brainstem, frontal-subcortical and limbic systems are extensively and reciprocally linked via neurotransmitter projection pathways. We argue that cognitive and behavioural features in patients with brainstem lesions reflect remote effects of brainstem structures on frontal lobe and limbic regions, as a consequence of disruption to ascending neurotransmitter pathways.

Peduncular hallucinosis

Peduncular hallucinosis (PH) is a syndrome of hallucinations and brainstem symptoms which has only been described in single case reports. A detailed analysis of five patients was undertaken to investigate the clincial characteristics, hallucinations and behavioural abnormalities of PH in greater detail. Frequent clinical symptoms were oculomotor disturbances, impaired arousal, dysarthria and ataxia. In the chronic stage, sleep-wake cycle disturbances were common. Hallucinations were naturalistic, complex, scenic, mostly visual, but also combined visual-acoustic or visual-tactile and recurred stereotypically over months. Patients experienced their hallucinations as genuine and were unable to discriminate their percepts from reality. Neuropsychological testing disclosed severe impairments of episodic memory, occasionally coupled with confabulatory behaviour. By contrast, memory for hallucinations remained intact. Deficits of attentional and executive functions were found in a subgroup of patients. Associated abnormal behaviours were common, comprising confusion, delusional misidentification for persons and places, and loss of disease awareness. PH appeared after focal lesions in various regions, such as the midbrain, thalamus and pons. These findings document that subcortical, brainstem-related hallucinations are vivid, recurring percepts that have a strong naturalistic character and are often associated with cognitive and behavioural abnormalities. It seems likely that brainstem hallucinosis is caused by damage to ascending reticular systems and thalamocortical circuits. Available observations suggest that PH compromises cognitive functions which enable us to differentiate between illusionary percepts and reality, a reality monitoring system.

Neuroimaging of serotonin uptake sites and antidepressant binding sites in the thalamus of humans and 'higher' animals

This review presents the results of in vitro, ex vivo and in vivo studies carried out primarily for identifying serotonin uptake sites and/or antidepressant binding sites in the brain of humans and 'higher' animals, namely nonhuman primates and pigs. Five lines of evidence are considered. First, studies carried out in vitro using synaptosomes or membrane preparations from human, nonhuman primate, and porcine brain have shown that certain thalamic nuclei are major sites of serotonergic neurotransmission in these species. Second, studies carried out in vitro or ex vivo using autoradiography or immunohistochemistry have indicated that the dorsomedial nucleus and some adjacent regions of the thalamus have a particularly high density of binding sites for antidepressant drugs that are selective serotonin reuptake inhibitors (SSRIs). Third, studies carried out in the living brain of nonhuman primates and pigs have found that SSRIs, radiolabeled for use in PET or SPECT, accumulate to a relatively high degree in midline and dorsal nuclei of the thalamus. Fourth, studies carried out using PET or SPECT radioligands in humans have demonstrated that regions in and around the dorsomedial nucleus of the thalamus are principal sites for accumulation of SSRIs. Fifth, studies of behavior of humans suffering from localized tissue damage in the thalamus have reported that symptoms of mania often occur in the patients, in accordance with the notion that an intact thalamus is required for normal regulation of mood. Taken together, the findings are consistent with the hypothesis that serotonergic neurotransmission in the dorsomedial nucleus of the thalamus could be causally involved in the pathophysiology of affective disease as well as in therapeutic actions of SSRIs.