Bimodal bilingualism is an individual or community's bilingual competency in at least one oral language and at least one sign language, which utilize two different modalities. An oral language consists of an vocal-aural modality versus a signed language which consists of a visual-spatial modality. A substantial number of bimodal bilinguals are children of deaf adults (CODA) or other hearing people who learn sign language for various reasons. Deaf people as a group have their own sign language(s) and culture that is referred to as Deaf, but invariably live within a larger hearing culture with its own oral language. Thus, "most deaf people are bilingual to some extent in [an oral] language in some form" In discussions of multilingualism in the United States, bimodal bilingualism and bimodal bilinguals have often not been mentioned or even considered, in part because American Sign Language, the predominant sign language used in the U.S., only began to be acknowledged as a natural language in the 1960s (in discussions of bimodal bilingualism in the U.S., the two languages involved are generally ASL and English). However, bimodal bilinguals share many of the same traits as traditional bilinguals (those with competency in at least two spoken languages), as well as differing in some interesting ways, due to the unique characteristics of the Deaf community. Bimodal bilinguals also experience similar neurological benefits as do unimodal bilinguals, with significantly increased grey matter in various brain areas and evidence of increased plasticity as well as neuroprotective advantages that can help slow or even prevent the onset of age-related cognitive diseases, such as Alzheimer's and dementia. Neurological implications and effects of bimodal bilingualism Most modern neurological studies of bilingualism employ functional neuroimaging techniques to uncover the neurological underpinnings of multilingualism and how multilingualism is beneficial to the brain. Neuroimaging and other neurological studies have demonstrated in recent years that multilingualism has a significant impact on the human brain. The mechanisms required by bilinguals to code-switch (that is, alternate rapidly between multiple languages within a conversation), not only demonstrate increased connectivity and density of the neural network in multilinguals, but also appear to provide protection against damage due to age and age-related pathologies, such as Alzheimer's. Multilingualism, especially bimodal multilingualism, can help slow to process of cognitive decline in aging. It is thought that this is a result of the increased work load that the executive system, housed mostly in the frontal cortex,