Dorsal White Matter Integrity and Name Retrieval in Midlife

A narrative review of the anatomy and function of the white matter tracts in language production and comprehension

Much is known about the role of cortical areas in language processing. The shift towards network approaches in recent years has highlighted the importance of uncovering the role of white matter in connecting these areas. However, despite a large body of research, many of these tracts’ functions are not well-understood. We present a comprehensive review of the empirical evidence on the role of eight major tracts that are hypothesized to be involved in language processing (inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, uncinate fasciculus, extreme capsule, middle longitudinal fasciculus, superior longitudinal fasciculus, arcuate fasciculus, and frontal aslant tract). For each tract, we hypothesize its role based on the function of the cortical regions it connects. We then evaluate these hypotheses with data from three sources: studies in neurotypical individuals, neuropsychological data, and intraoperative stimulation studies. Finally, we summarize the conclusions supported by the data and highlight the areas needing further investigation.

Older and Wiser: Interpretation of Proverbs in the Face of Age-Related Cortical Atrophy

In the present study, we investigated whether interpretation of proverbs differs across the lifespan and if so, whether it is associated with age-related fronto-temporal atrophy. Using a sample of 333 healthy individuals aged 18–89 years, we found a significant effect of age on proverb interpretation [H(2) = 12.001, p = 0.002]: old adults (OA) were better than young adults (YA) (p = 0.002), and so were middle-aged-adults (MA) (p = 0.005). OA and MA had significantly less grey matter (GM) than YA in frontal and temporal lobes bilaterally, and OA less than MA in the right temporal lobe. GM volumes in these regions did not moderate the effect of age on the proverbs scores. The whole-brain analysis of groups’ GM maps revealed that the proverbs scores were associated with more GM in YA relative to OA in the right middle temporal gyrus, which is consistent with evidence on the role of this area in processing of unfamiliar proverbs. Overall, our data suggest that interpretation of proverbs is well preserved in late adulthood, despite considerable age-related cortical atrophy.

Association between scrub typhus encephalitis and diffusion tensor tractography detection of Papez circuit injury: A case report

BACKGROUND

It is difficult to restore the cognitive functions of patients with impaired cognition caused by brain injury. Diffusion tensor imaging can visualize the integrity of neural tracts in the white matter (WM) three-dimensionally. It is unclear whether encephalitis following scrub typhus damages the WM. For the first time, we aimed to report diffusion tensor tractography (DTT) findings in a chronic patient with cognitive impairment following scrub typhus encephalitis, which revealed injury to the Papez circuit of the WM.

CASE SUMMARY

A 70-year-old male patient was affected by encephalitis caused by scrub typhus that occurred 23 years ago. He had poor cognition and his clinical examination findings were as follows: Mini-Mental Status Examination score, 14; and handgrip strength (right/left, kg), 32.3/31.3. DTT revealed serious injuries of the left thalamocingulate tract and right mammillothalamic tract in the Papez circuit, and a partial injury of the anterior part of the fornix.

CONCLUSION

Using DTT, we found a relationship between cognitive impairment and the integrity of the Papez circuit following scrub typhus.

Strategies to resolve recall failures for proper names: New data

Personal names are particularly susceptible to retrieval failures. Studies describing people's spontaneous strategies for resolving such failures have indicated that people frequently search for semantic or contextual information about the target person. However, previous experimental studies have shown that, while providing phonological information may help resolve a name-recall failure, by contrast, providing semantic information is usually not helpful. In the first study, in order to reduce a bias present in previous studies of spontaneous strategies, explicit instructions were given to participants, specifying that the focus of the study was on a voluntary search for information. Participants reported strategically searching for semantic/contextual strategies when they tried to resolve a name-retrieval failure more often than they reported searching for phonological/orthographic information. In addition, phonological/orthographic strategies were perceived as more difficult than semantic/contextual strategies. In a second experiment, we investigated whether retrieving phonological information by oneself is objectively difficult in a face-naming task: in the event of retrieval failure, participants were instructed to search for phonological information in some trials and for semantic information in other trials. Participants recalled semantic information in 94% of the trials when instructed to search for semantic information. By contrast, when instructed to search for phonological information, participants remained unable to recall any correct piece of phonological information in about 55% of the trials. This result shows that the retrieval of phonological information is objectively difficult. This difficulty could explain why people do not privilege searching for phonology to resolve name-retrieval failures.