Integrative Models of Broca's Area and the Ventral Premotor Cortex

Unraveling the Thread of Aphasia Rehabilitation: A Translational Cognitive Perspective

Translational neuroscience is a multidisciplinary field that aims to bridge the gap between basic science and clinical practice. Regarding aphasia rehabilitation, there are still several unresolved issues related to the neural mechanisms that optimize language treatment. Although there are studies providing indications toward a translational approach to the remediation of acquired language disorders, the incorporation of fundamental neuroplasticity principles into this field is still in progress. From that aspect, in this narrative review, we discuss some key neuroplasticity principles, which have been elucidated through animal studies and which could eventually be applied in the context of aphasia treatment. This translational approach could be further strengthened by the implementation of intervention strategies that incorporate the idea that language is supported by domain-general mechanisms, which highlights the impact of non-linguistic factors in post-stroke language recovery. Here, we highlight that translational research in aphasia has the potential to advance our knowledge of brain-language relationships. We further argue that advances in this field could lead to improvement in the remediation of acquired language disturbances by remodeling the rationale of aphasia-therapy approaches. Arguably, the complex anatomy and phenomenology of aphasia dictate the need for a multidisciplinary approach with one of its main pillars being translational research.

Disruption of Broca's Area Alters Higher-order Chunking Processing during Perceptual Sequence Learning

Because Broca's area is known to be involved in many cognitive functions, including language, music, and action processing, several attempts have been made to propose a unifying theory of its role that emphasizes a possible contribution to syntactic processing. Recently, we have postulated that Broca's area might be involved in higher-order chunk processing during implicit learning of a motor sequence. Chunking is an information-processing mechanism that consists of grouping consecutive items in a sequence and is likely to be involved in all of the aforementioned cognitive processes. Demonstrating a contribution of Broca's area to chunking during the learning of a nonmotor sequence that does not involve language could shed new light on its function. To address this issue, we used offline MRI-guided TMS in healthy volunteers to disrupt the activity of either the posterior part of Broca's area (left Brodmann's area [BA] 44) or a control site just before participants learned a perceptual sequence structured in distinct hierarchical levels. We found that disruption of the left BA 44 increased the processing time of stimuli representing the boundaries of higher-order chunks and modified the chunking strategy. The current results highlight the possible role of the left BA 44 in building up effector-independent representations of higher-order events in structured sequences. This might clarify the contribution of Broca's area in processing hierarchical structures, a key mechanism in many cognitive functions, such as language and composite actions.

Manual praxis in stone tool manufacture: implications for language evolution

Alternative functions of the left-hemisphere dominant Broca's region have induced hypotheses regarding the evolutionary parallels between manual praxis and language in humans. Many recent studies on Broca's area reveal several assumptions about the cognitive mechanisms that underlie both functions, including: (1) an accurate, finely controlled body schema, (2) increasing syntactical abilities, particularly for goal-oriented actions, and (3) bilaterality and fronto-parietal connectivity. Although these characteristics are supported by experimental paradigms, many researchers have failed to acknowledge a major line of evidence for the evolutionary development of these traits: stone tools. The neuroscience of stone tool manufacture is a viable proxy for understanding evolutionary aspects of manual praxis and language, and may provide key information for evaluating competing hypotheses on the co-evolution of these cognitive domains in our species.

From gestures to words: spontaneous verbal labeling of complex sequential hand movements reduces fMRI activation of the imitation-related regions

The association of verbal labels with visuo-spatial patterns and sequences detectably alters neuronal activity in the brain in ways that have yet to be fully characterized. This study investigated the neural substrates involved in the effect of spontaneous verbal labeling on memorizing increasingly complex sequences of hand movements. We used functional magnetic resonance imaging (fMRI) to test our hypothesis that when verbal labels were employed, neuronal activity in imitation-related regions, such as the left inferior frontal gyrus (IFG), would be reduced, whereas without verbal labels, neuronal activation would increase. Sixteen healthy adults satisfactorily performed an immediate imitation task involving six levels of increasing complexity. After the fMRI experiment, participants reported at which complexity level they had formed verbal labels. Based on the self-report, we categorized the task blocks at each complexity level as either with verbal labeling (VL+) or without (VL-). Compared with VL+, the VL- condition activated the left IFG, bilateral middle frontal gyri, left precentral gyrus, and the right angular gyrus, whereas the opposite contrast revealed no significant brain activation. Verbal labeling seems to serve as an efficient heuristic that reduces the cost of cortical activation in the imitation-related regions.

Behavioral patterns and lesion sites associated with impaired processing of lexical and conceptual knowledge of actions

To further investigate the neural substrates of lexical and conceptual knowledge of actions, we administered a battery of six tasks to 226 brain-damaged patients with widely distributed lesions in the left and right cerebral hemispheres. The tasks probed lexical and conceptual knowledge of actions in a variety of verbal and non-verbal ways, including naming, word-picture matching, attribute judgments involving both words and pictures, and associative comparisons involving both words and pictures. Of the 226 patients who were studied, 61 failed one or more of the six tasks, with four patients being impaired on the entire battery, and varied numbers of patients being impaired on varied combinations of tasks. Overall, the 61 patients manifested a complex array of associations and dissociations across the six tasks. The lesion sites of 147 of the 226 patients were also investigated, using formal methods for lesion-deficit statistical mapping and power analysis of lesion overlap maps. Significant effects for all six tasks were found in the following left-hemisphere regions: the inferior frontal gyrus; the ventral precentral gyrus, extending superiorly into what are likely to be hand-related primary motor and premotor areas; and the anterior insula. In addition, significant effects for 4-5 tasks were found in not only the regions just mentioned, but also in several other left-hemisphere areas: the ventral postcentral gyrus; the supramarginal gyrus; and the posterior middle temporal gyrus. These results converge with previous research on the neural underpinnings of action words and concepts. However, the current study goes considerably beyond most previous investigations by providing extensive behavioral and lesion data for an unusually large and diverse sample of brain-damaged patients, and by incorporating multiple measures of verb comprehension. Regarding theoretical implications, the study provides new support for the Embodied Cognition Framework, which maintains that conceptual knowledge is grounded in sensorimotor systems.

Wie wir unser motorisches System nutzen, um Ereignisse vorherzusagen

Zusammenfassung. Imitieren oder im Wortsinne nach-vollziehen können wir weder unbelebte Ereignisse, wie etwa anbrandende Meereswellen, noch nicht-humane belebte, wie einen vorbeilaufenden Hund. Wir können aber antizipieren, wie sie sich entwickeln, und neuere Studien zeigen, dass dabei unser motorisches System aktiv ist. Diese Phänomene sind erklärlich, wenn man eine prädiktive Darstellung des motorischen Systems von der Handlungs- auf die Ereignis-Wahrnehmung generalisiert. Demnach sagen wir Ereignisse, die wir nicht selber reproduzieren können, auf der Grundlage audio- und visuo-motorischer Repräsentationen vorher, die ihrerseits niemals einer tatsächlichen Handlung entsprechen, weil ihnen propriozeptive und andere interozeptive Informationen fehlen. Diese Perspektive regt zu einer neuen Sichtweise auf das überkommene Konzept des „motorischen” Systems an.

Neural reuse and cognitive homology

Neural reuse theories suggest that, in the course of evolution, a brain structure may acquire or lose a number of cognitive uses while maintaining its cognitive workings (or low-level operations) fixed. This, in turn, suggests that homologous structures may have very different cognitive uses, while sharing the same workings. And this, essentially, is homology thinking applied to brain function.

Functional specializations for music processing in the human newborn brain

In adults, specific neural systems with right-hemispheric weighting are necessary to process pitch, melody, and harmony as well as structure and meaning emerging from musical sequences. It is not known to what extent the specialization of these systems results from long-term exposure to music or from neurobiological constraints. One way to address this question is to examine how these systems function at birth, when auditory experience is minimal. We used functional MRI to measure brain activity in 1- to 3-day-old newborns while they heard excerpts of Western tonal music and altered versions of the same excerpts. Altered versions either included changes of the tonal key or were permanently dissonant. Music evoked predominantly right-hemispheric activations in primary and higher order auditory cortex. During presentation of the altered excerpts, hemodynamic responses were significantly reduced in the right auditory cortex, and activations emerged in the left inferior frontal cortex and limbic structures. These results demonstrate that the infant brain shows a hemispheric specialization in processing music as early as the first postnatal hours. Results also indicate that the neural architecture underlying music processing in newborns is sensitive to changes in tonal key as well as to differences in consonance and dissonance.

Lost in localization: the need for a universal coordinate database

One of the great advantages of neuroimaging research is the use of an established and uniform coordinate system. This 3-D coordinate system allows for the comparison of activation locations across studies. In order to capitalize upon this advantage, however, researchers must be able to find relevant studies based upon activation locations. A number of research groups have embarked upon solutions to this problem, but to date there exists no exhaustive, universal coordinate database. In this commentary we outline the nature of the problem, its current solutions, and propose alternate solutions. We close with suggestions on how those in the field can facilitate the process of developing a universal coordinate database.

Knowledge of the Semantic Constraints on Adjective Order Can Be Selectively Impaired

When multiple adjectives are used to modify a noun, they tend to be sequenced in the following way according to semantic class: value > size > dimension > various physical properties > color. To investigate the neural substrates of these semantic constraints on adjective order, we administered a battery of three tests to 34 brain-damaged patients and 19 healthy participants. Six patients manifested the following performance profile. First, they failed a test that required them to discriminate between semantically determined correct and incorrect sequences of adjectives-e.g., thick blue towel vs. *blue thick towel. Second, they passed a test that assessed their knowledge of two purely syntactic aspects of adjective order-specifically, that adjectives can precede nouns, and that adjectives can precede other adjectives. Finally, they also passed a test that assessed their knowledge of the categorical (i.e., class-level) features of adjective meanings that interact with the semantic constraints underlying adjective order-e.g., that thick is a dimensional adjective and that blue is a color adjective. Taken together, these behavioral findings suggest that the six patients have selectively impaired knowledge of the abstract principles that determine how different semantic classes of adjectives are typically mapped onto different syntactic positions in NPs. To identify the neuroanatomical lesion patterns that tend to correlate with defective processing of adjective order, we combined lesion data from the six patients just described with lesion data from six other patients who we reported in a previous study as having similar impairments [Kemmerer, D. (2000). Selective impairment of knowledge underlying adjective order: Evidence for the autonomy of grammatical semantics. Journal of Neurolinguistics, 13, 57-82.] We found that the most common areas of damage included the left posterior inferior frontal gyrus and the left inferior parietal lobule. Overall, these results shed new light on the neural substrates of the syntax-semantics interface.

Neuroanatomical distribution of five semantic components of verbs: evidence from fMRI

The Simulation Framework, also known as the Embodied Cognition Framework, maintains that conceptual knowledge is grounded in sensorimotor systems. To test several predictions that this theory makes about the neural substrates of verb meanings, we used functional magnetic resonance imaging (fMRI) to scan subjects' brains while they made semantic judgments involving five classes of verbs-specifically, Running verbs (e.g., run, jog, walk), Speaking verbs (e.g., shout, mumble, whisper), Hitting verbs (e.g., hit, poke, jab), Cutting verbs (e.g., cut, slice, hack), and Change of State verbs (e.g., shatter, smash, crack). These classes were selected because they vary with respect to the presence or absence of five distinct semantic components-specifically, ACTION, MOTION, CONTACT, CHANGE OF STATE, and TOOL USE. Based on the Simulation Framework, we hypothesized that the ACTION component depends on the primary motor and premotor cortices, that the MOTION component depends on the posterolateral temporal cortex, that the CONTACT component depends on the intraparietal sulcus and inferior parietal lobule, that the CHANGE OF STATE component depends on the ventral temporal cortex, and that the TOOL USE component depends on a distributed network of temporal, parietal, and frontal regions. Virtually all of the predictions were confirmed. Taken together, these findings support the Simulation Framework and extend our understanding of the neuroanatomical distribution of different aspects of verb meaning.