When only the right hemisphere is left: Studies in language and communication.

An adult of above normal intelligence, BL, underwent left hemispherectomy at age five, and subsequently graduated from college and has been regularly employed. Using standardized neuropsychological instruments, previous extensive testing had revealed optimal performance for a hemispherectomized subject. To probe communicative abilities in greater detail, and to examine current questions about linguistic superiority of the left hemisphere and "crowding" of right hemisphere functions, 12 additional protocols were administered. BL performed at normal or above on nearly all protocols. However, performance on production of phonemically complex words was effortful, and deficits were seen on two tests requiring comprehension of linguistic contrasts in prosody (Linguistic Prosody Test) and syntax (the Active–Passive Test). These findings support previous claims of reduced ability in specific, circumscribed linguistic functions in the left hemispherectomized person, and lead to suggestions for further testing of communicative competence in individuals with a single intact hemisphere.

Regarding speech, language, and communicative function, BL’s performance appears grossly normal in pronunciation, grammar, semantics, and usage. By the language rating system devised by Curtiss et al. (2001), our findings are in agreement with theirs; using this ranking scale, they found no effect of left versus right hemisphere removal. Thus, this study of BL, a left hemispherectomized individual with the highest spontaneous speech rating, agrees with their failure to confirm an effect of left hemisphere removal on language, as measured by their Spoken Language Scale. However, focused speech and language testing performed on BL did uncover linguistic deficits. On motor speech testing, increased effort was noted for production of phonemically complex phrases. In findings that may support this perspective, greater impairments on reading and spelling following left than right hemispherectomy were reported. To discover relative speech production deficits in abnormal populations, tests especially designed to challenge linguistic competence are likely necessary.

In BL, from the array of evaluation protocols administered in this and previous testing, frank diminution in performance was seen only on tests which involved subtle linguistic contrasts. Note that the deficient linguistic-prosodic performance was observed in the comprehension, not the production subtest. This score discrepancy (higher performance on production than comprehension of the test items) was also observed in normal subjects. These observations suggest that in some domains of language competence, comprehension may be a subtler probe of the intrinsic linguistic ability of the left hemisphere than production. Our findings for the comprehension tasks are in agreement with Stark, Bleile, Brandt, Freeman, and Vining (1995), who reported greater deficits in subjects following left- than right-hemispherectomy, using syntactic comprehension and rapid-rate auditory processing.

On both of the linguistic-contrast measures utilizing a comprehension mode (prosodic and active–passive contrasts), BL exhibited abilities more consistent with performance at an earlier developmental stage, suggesting that although his production competence as observed in spontaneous speech represented a "mature grammar," his comprehension competence did not.

Regarding the Active–Passive test, there has been controversy in linguistic theory about the active–passive contrast, 4 and the negative particle ("not"). The debate has questioned whether these are primarily syntactic or semantic elements. In some approaches, the demarcation between syntax and semantics is less distinct. Whatever the perspective, the developmental data reported by Dennis and Kohn (1985) suggest that younger children make more errors on the negative examplars of both active and passive voice, while in older children, active sentences, whether affirmative or negative, show similar accuracy scores, (higher than passive sentences). BL’s accuracy scores reveal a pattern similar to that of younger children (ages 6 and 8).

BL performed better than the normal-control group on same- and other-race famous names/faces; therefore, no deficits in personal relevance, associated in other studies with intact right hemisphere function, are suspected.

Communicative abilities of the right cerebral hemisphere more recently proposed, such as personal relevance especially as seen in famous proper noun recognition, the various functions of prosody and voice recognition, unique lexical semantics including emotional words and topics within pragmatic studies such as nonliteral language, maintenance of topic, and humor, and other aspects of social discourse remain to be investigated in more depth in persons with a single hemisphere.

By our casual observation in social situations, such as dinner at restaurants and site seeing, BL’s socially exhibited prosodic and pragmatic language skills, including grasp of situational context, conversation, interactional humor, and turn taking, were fully intact. However, although grammatical competence also appeared informally intact, formal testing suggested a diminution, and therefore it is possible that deficits suggesting subtle effects of crowding might be seen also when pragmatic communicative abilities are carefully tested by well designed instruments.

Although subtle linguistic deficits were uncovered in two carefully constructed comprehension tasks and in formal clinical speech testing, the otherwise above normal language abilities of BL challenge the usual understanding of hemispheric specialization of function. The possibility that BL was "naturally left handed," developing language in the right hemisphere, cannot be completely eliminated. From the medical history, left hemispheric damage was likely perinatal in etiology. Statistics weigh against predisposed left handedness in BL, and he was reported to be speaking with severe dysarthria until his damaged left hemisphere was removed, indicating a significant role of the left hemisphere in speech in early development. However, his rapid postsurgical recovery of normal speech and language behavior indicates at least early readiness of the right hemisphere for linguistic communication. This, in fact, could reflect the normal condition. Maturational schedules for establishment of laterality are not well understood and it is not clear which hemisphere predominates for what kinds of language behaviors at different early phases of child language acquisition, but a role of the right hemisphere at the earliest stages has been suggested by behavioral, electrophysiological, and functional imaging studies.

However well attested is lateralization of speech and language function to the left hemisphere with the accompanying right handedness, how and why this happens has not been explained. A genetic explanation will have difficulty with the simplistic question that arises: in the hemispherectomized person, how does the developing right hemisphere "know" that the left hemisphere is not going to do this work? Perhaps the "demands of several levels of interpersonal communication underlying language" actuated by gesturing and triggering cerebral asymmetry are responsive to changes brought about by motor insufficiencies of the damaged hemisphere. Another proposal considers plasticity to be a mechanism that governs cognitive priorities.

The answer to the question posed by Code, 1996 and Code, 1997: "Can the right hemisphere speak?" is "yes," to lesser or greater extent, when given autonomy in the developing brain, because of damage to or removal of the left hemisphere but only very little in the normally developed brain or when the left hemisphere can play even a severely reduced role, as seen in children as well as in aphasia patients. These observations impinge on unanswered questions about the role of the left hemisphere in inhibiting the right.

The scenario whereby one hemisphere relatively successfully takes over the functions of two does not provide support to current notions of "modules" of cognitive function in the mind with their implied predictable correspondence to specifiable brain structures. Given the achievement of the single, nondominant hemisphere in language competence, the mystery of human language development in ontogeny and phylogeny cannot be convincingly unmasked by the proposal of a species-unique "language organ", unless this is meant as a metaphor without implied cerebral localization or predicted, definable anatomical properties. Notions of the corpus callosum as essential communication link between functional systems, enabling human behavior, and the search for self-recognition abilities of the left hemisphere or of the right hemisphere, as essential for self-awareness might well gain a different perspective from observations of BL and other hemispherectomized persons with full adult competence.

The numerous observations on cognitively intact persons hemispherectomized in childhood bring to mind the report of Lorber (1983) on hydrocephalic adults, whose brains are constituted of only a thin layer of cerebral tissue, and yet who enjoy normal or superior motor and cognitive abilities. Although "localization of function" has been a useful heuristic for analysis of brain–behavior correlations, factors contributing to "cerebral plasticity" are complex and powerful, and remain to be understood.