Artificial intelligence, especially large language models (LLMs), is reshaping how we learn, communicate, and create. These systems provide students and professionals immediate access to fluent, context-aware language that can support learning, increase productivity, and spark creativity. But what happens when their use becomes excessive? This paper explores the potential long-term consequences of over-relying on LLMs—particularly memory, critical thinking, creativity, and motivation. Drawing on research in cognitive psychology, education, neuroscience, and media studies, it argues that LLMs are best understood as cognitive prostheses: incredibly valuable when used wisely, but risky when they replace rather than support human imagination.