Subcortical functions in language: A working model

The current paper explains a model of subcortical language functions that focuses on dynamic interactions between the cortex, the thalamus, and the basal ganglia in the production of spoken language. The model was derived from (a) studies of subcortical lesions and language, (b) studies of subcortical stimulation and language, (c) knowledge regarding neural pathways between various cortical and subcortical structures, and (d) indications that preverbal monitoring of language occurs. In the current model, the thalamus plays roles in cortical arousal and activation and in preverbal semantic monitoring. The basal ganglia function to regulate the degree of excitation conveyed from the thalamus to the cortex and to time the release of formulated language for motor programming. Consistency with classical syndromes of aphasia and potential applications to other areas in the neurosciences are discussed. The current theory, unlike previous formulations, is specific enough that testable hypotheses can be derived.     

Category-Specific Naming Deficit for Medical Terms after Dominant Thalamic/Capsular Hemorrhage

Postmortem, retrograde degeneration, and electrical stimulation studies have implicated the anterior pulvinar in language processing. We examined a patient who, after a hemorrhage affecting the dominant pulvinar and internal capsule, exhibited a circumscribed anomia for medical items and conditions. No other language disturbance was noted. Five category-specific word lists, matched for word frequency, were administered in a naming-to-definition format. Results indicated that the patient exhibited a significant category-specific naming deficit for medical items and conditions compared to matched control subjects. Although medical item lists were found to differ from nonmedical item lists in imageability and abstractness, B.C.'s category-specific deficit did not seem to be caused by word frequency, concept familiarity, imageability, or abstractness. Nor could the patient's performance be explained on the basis of deficits in broader semantic classifications (i.e., animate vs inanimate or man-made vs natural). The patient was unable to retrieve medical items even when given phonemic cues for those he could not name. Findings indicate that subtotal damage in the dominant pulvinar may create category-specific deficits.     

Middle School Learners' Use of Latin Roots to Infer the Meaning of Unfamiliar Words

This study investigated how middle school students leverage information about bound Latin roots (e.g., voc in advocate and vociferous) to infer meanings of unfamiliar words, and how instruction may facilitate morphological analysis using roots. A dynamic assessment of morphological analysis was administered to 29 sixth graders (n = 17 intervention students) and 30 seventh graders (n = 18 intervention students). Qualitative analyses of analytic strategies revealed patterns of morphological problem solving that included direct (i.e., direct application of roots to analyze unfamiliar words) and indirect routes (i.e., use of known words that carry the roots to analyze unfamiliar words). Intervention students applied a direct route at higher rates than control students. Correlational analyses revealed a small but significant treatment effect on establishing meaning memory representations for roots and a significant, positive treatment effect for use of roots to infer unfamiliar word meanings. Overall results show promise for use of bound Latin roots for morphological problem solving.     

Subcortical Aphasia

We critically review the literature on subcortical aphasia, suggest that a number of traditional concepts regarding mechanisms of aphasia are inconsistent with now abundant data, and propose several new hypotheses. The absence of aphasia in 17 reported cases of dominant hemisphere striatocapsular infarction and the finding of nearly every conceivable pattern of language impairment in 33 different reported cases of striatocapsular infarction provide strong evidence against a major direct role of the basal ganglia in language and against disconnection or diaschisis as mechanisms of nonthalamic subcortical aphasia. However, detailed consideration of the vascular events leading to striatocapsular infarction strongly suggests that associated linguistic deficits are predominantly related to sustained cortical hypoperfusion and infarction not visible on structural imaging studies. Thalamic disconnection, as may occur with striatocapsular infarcts with extension to the temporal stem and putamenal hemorrhages, may also contribute to the language deficits in some patients. Review of the literature on thalamic infarction, in conjunction with previously unreported anatomic details of four cases, suggests that what infarcts in the tuberothalamic artery territory and the occasional infarcts in the paramedian artery territory associated with aphasia have in common is damage to the frontal lobe–inferior thalamic peduncle–nucleus reticularis–center median system that may be involved in regulating the thalamic gate in attentional processes. Disruption of attentional gating in the pulvinar and lateral posterior nuclei resulting from such lesions may impair selection of specific neuronal networks in the projection field of these nuclei that serve as the substrate for lexical–semantic function, which is in effect a disruption of a type of working memory, as defined by Goldman–Rakic. We define this as a defect of selective engagement.     

Subcortical mechanisms in language: lexical-semantic mechanisms and the thalamus.

Four previously published cases of dominant thalamic lesion in which the author has participated are reviewed to gain a better understanding of thalamic participation in lexical-semantic functions. Naming deficits in two cases support Nadeau and Crosson's (1997) hypothesis of a selective engagement mechanism involving the frontal lobes, inferior thalamic peduncle, nucleus reticularis, and other thalamic nuclei, possibly the centromedian nucleus. This mechanism selectively engages those cortical areas required to perform a cognitive task, while maintaining other areas in a state of relative disengagement. Deficits in selective engagement disproportionately affect lexical retrieval based on semantic input, as opposed to lexical and sublexical processes, because the former is more dependent upon this attentional system. The concept of selective engagement is also useful in understanding thalamic participation in working memory, as supported by data from one recent functional neuroimaging study. Other processes also may be compromised in more posterior thalamic lesions which damage the pulvinar but not other components of this selective engagement system. A third case with aphasia after a more superior and posterior thalamic lesion also had oral reading errors similar to those in neglect dyslexia. The pattern of deficits suggested a visual processing problem in the early stages of reading. The fourth case had a category-specific naming deficit after posterior thalamic lesion. Taken together, the latter two cases indicate that the nature of language functions in more posterior regions of the dominant thalamus depends upon the cortical connectivity of the thalamic region. Together, findings from the four cases suggest that thalamic nuclei and systems are involved in multiple processes which directly or indirectly support cortical language functions.     

When to Take Up Roots: The Effects of Morphology Instruction for Middle School and High School English Learners

A majority of the challenging words that adolescent readers encounter in school texts are morphologically complex and from the Latinate layer of English. For these words, bound roots carry important meaning, such as the relation between innovative and its bound root, nov, meaning “new.” This study investigated the effects of instruction about bound Latin roots on academic word learning and morphological problem-solving skill with English Learners (EL) at three grade bands: Grades 6–8, 9–10, and 11–12. Employing a within-subjects design, 82 students participated in two counterbalanced intervention conditions: an academic vocabulary without morphology (comparison condition) and a morphology-focused academic vocabulary intervention (treatment condition). The largest treatment effects were observed for oldest students, but positive effects were observed at all grade levels. Results suggest that instruction focused on the major meaning-carrying components of academic words of the Latinate layer in English—bound roots—is especially effective for ELs in the secondary grades.     

Uneven Profiles: Language Minority Learners' Word Reading, Vocabulary, and Reading Comprehension Skills

English reading comprehension skill development was examined in a group of 87 native Spanish-speakers developing English literacy skills, followed from fourth through fifth grade. Specifically, the effects of Spanish (L1) and English (L2) oral language and word reading skills on reading comprehension were investigated. The participants showed average word reading skills and below average comprehension skills, influenced by low oral language skills. Structural equation modeling confirmed that L2 oral language skills had a large, significant effect on L2 reading comprehension, whereas students' word-level reading skills, whether in L1 or L2, were not significantly related to English reading comprehension in three of four models fitted. The results converge with findings from studies with monolinguals demonstrating the influence of oral language on reading comprehension outcomes, and extend these findings by showing that, for language minority learners, L2 oral language exerts a stronger influence than word reading in models of L2 reading.     

Verbal Memory Abilities of Children With Brain Tumors

Several critical neuroanatomical structures and pathways for memory performance are located in the third ventricle region. This led us to predict that verbal memory abilities would be more impaired in children treated for third ventricle tumors compared to those treated for cerebellar tumors. Archival data was obtained from 24 pediatric patients with third ventricle region tumors and 18 pediatric patients with cerebellar tumors. Neuroradiological verifications of tumor involvement and hydrocephalus severity (i.e., Evans Index) on preoperative scans and MRIs proximal to the time of the neuropsychological evaluation were conducted. The potential confounds of hydrocephalus severity, seizure medication, age, radiation treatment, and chemotherapy were addressed. Verbal IQ was comparable between tumor groups and in the Average range. The third ventricle region group performed significantly worse on list learning and delayed list recall compared to the cerebellar group. Their mean performance was in the clinically impaired range on both trials. The third ventricle region tumor group performed better than the cerebellar tumor group on Digit Span, a basic repetition, attention span task. These findings support the hypothesis that pediatric patients with third ventricle region brain tumors are more likely to be impaired on verbal recall tasks compared to pediatric patients with cerebellar brain tumors. In contrast, patients who were treated for cerebellar tumors were more impaired on the basic repetition, attention span task compared to patients who were treated for third ventricle tumors. Future studies should examine the specific neuroanatomical structures and pathways that are damaged and may influence differential cognitive impairments in children.