Syndromes of Cognitive Dysfunction

Cognitive function refers to the mental process of knowing things. It includes high-level cortical functions such as memory, language, perception, and executive function (planning, initiating, and reasoning) that generally depend on the alert state and focused attention. Dysfunction of cognition without a change in consciousness may result in various disorders, including aphasia, apraxia, agnosia, executive dysfunction, and memory disorders such as dementia and amnesia. Transient dysfunction of cognition associated with a change in level of consciousness or attention may be due to delirium or confusional states. This chapter broadly introduces the specific definitions of cognitive dysfunction and the overall differential diagnoses.

Understanding diaschisis models of attention dysfunction with rTMS

Visual attentive tracking requires a balance of excitation and inhibition across large-scale frontoparietal cortical networks. Using methods borrowed from network science, we characterize the induced changes in network dynamics following low frequency (1 Hz) repetitive transcranial magnetic stimulation (rTMS) as an inhibitory noninvasive brain stimulation protocol delivered over the intraparietal sulcus. When participants engaged in visual tracking, we observed a highly stable network configuration of six distinct communities, each with characteristic properties in node dynamics. Stimulation to parietal cortex had no significant impact on the dynamics of the parietal community, which already exhibited increased flexibility and promiscuity relative to the other communities. The impact of rTMS, however, was apparent distal from the stimulation site in lateral prefrontal cortex. rTMS temporarily induced stronger allegiance within and between nodal motifs (increased recruitment and integration) in dorsolateral and ventrolateral prefrontal cortex, which returned to baseline levels within 15 min. These findings illustrate the distributed nature by which inhibitory rTMS perturbs network communities and is preliminary evidence for downstream cortical interactions when using noninvasive brain stimulation for behavioral augmentations.

Effects of transcranial magnetic stimulation on the performance of the activities of daily living and attention function after stroke: a randomized controlled trial

Objective: We aimed to interrogate the effects of transcranial magnetic stimulation (TMS) on the performance in activities of daily living (ADL) and attention function after stroke. Design: Randomized controlled trial. Setting: Inpatient rehabilitation hospital. Subjects: We randomized 62 stroke patients with attention dysfunction who were randomly assigned into two groups, and two dropped out from each group. The TMS group ( n = 29) and a sham group ( n = 29), whose mean (SD) was 58.12 (6.72) years. A total of 33 (56.9%) patients had right hemisphere lesion while the rest 25 (43.1%) patients had left hemisphere lesion. Interventions: Patients in the TMS group received 10 Hz, 700 pulses of TMS, while those in the sham group received sham TMS for four weeks. All the participants underwent comprehensive cognitive training. Main measures: At baseline, and end of the four-week treatment, the performance in the activities of daily living was assessed by Functional Independence Measure (FIM). On the other side, attention dysfunction was screened by Mini-Mental State Examination (MMSE), while the attention function was assessed by the Trail Making Test-A (TMT-A), Digit Symbol Test (DST) and Digital Span Test (DS). Results: Our data showed a significant difference in the post-treatment gains in motor of Functional Independence Measure (13.00 SD 1.69 vs 4.21 SD 2.96), cognition of Functional Independence Measure (4.69 SD 1.56 vs 1.52 SD 1.02), total of Functional Independence Measure (17.69 SD 2.36 vs 5.72 SD 3.12), Mini-Mental State Examination (3.07 SD 1.36 vs 1.21 SD 0.62), time taken in Trail Making Test-A (96.67 SD 25.18 vs 44.28 SD 19.45), errors number in Trail Making Test-A (2.72 SD 1.03 vs 0.86 SD 1.03), Digit Symbol Test (3.76 SD 1.09 vs 0.76 SD 0.87) or Digital Span Test (1.69 SD 0.54 vs 0.90 SD 0.72) between the TMS group and the sham group ( P < 0.05). Conclusions: Taken together, we demonstrate that TMS improves the performance in the activities of daily living and attention function in patients with stroke.

Structural Brain Correlates of Attention Dysfunction in Lewy Body Dementias and Alzheimer’s Disease

Lewy body dementia (LBD) and Alzheimer’s disease (AD) are common forms of dementia that have different clinical profiles but are both commonly associated with attentional deficits. The aim of this study was to investigate efficiency of different attentional systems in LBD and AD and its association with brain structural abnormalities.We studied reaction time (RT) data from 45 LBD, 31 AD patients, and 22 healthy controls using the Attention Network Test to assess the efficiency of three different attentional system: alerting, orienting, and executive conflict. Voxel-based morphometry was used to investigate relations between different attention components and cortical volume.Both dementia groups showed slower overall RTs than controls, with additional slowing in LBD relative to AD. There was a significant alerting effect in controls which was absent in the dementia groups, the executive conflict effect was greater in both dementia groups compared to controls, but the orienting effect did not differ between groups. Mean RT in AD was negatively correlated with occipital grey matter volume and in LBD orienting efficiency was negatively related to occipital white matter volume. Given that previous studies in less impaired patients suggest a maintenance of the alerting effect, the absent alerting effect in our study suggests a loss of alerting efficiency with dementia progression. While orienting was largely preserved, it might be related to occipital structural abnormalities in LBD. Executive function was markedly impaired in both dementia groups, however, the absence of relations to brain volume suggests that it might be more related to functional rather than macrostructural pathophysiological changes.