手書き想像して文字入力　まひの患者助ける脳インプラント技術

【東京ＡＦＰ＝時事】首から下がまひした男性が、画面を食い入るように見つめている。男性が手で文字を書くのを想像すると、その文字が画面にタイプされて現れる。（写真はまひのある人が文字を書くのを想像すると、その文字が画面にタイプされるシステムについて説明した図）
　６５歳のこの男性が「タイプ」する速さは、同世代の人がスマートフォンで文字を打つのとほぼ同じだ。これを可能にしているのは、新たな脳インプラント技術だ。
　この研究に関する論文が１２日、英科学誌ネイチャーに掲載された。論文の筆頭著者で、米スタンフォード大学の科学者フランク・ウィレット氏は、同研究は脊髄損傷や脳卒中、運動ニューロン疾患の患者に恩恵をもたらすことができるだろうと語る。
　体がまひした患者のための既存の装置は、眼球の動きや、カーソルを動かして文字をポイント・クリックするイメージに頼ってきた。
　だがウィレット氏率いるチームは、文字の手書きを思い浮かべることによっても、思いを表現することができるかもしれないと考えた。
　研究は「Ｔ５」とニックネームが付けられた男性を対象に行われた。男性は２００７年に脊髄に損傷を受け、首から下がまひしている。
　「Ｔ５」の左脳に、錠剤ほどの大きさのブレーン・コンピューター・インターフェース（ＢＣＩ）チップ二つが取り付けられた。これにより、手の動きをつかさどる運動野でのニューロンの発火が検知できる。
　出された信号はセンサーによってコンピューターに伝達され、ＡＩ（人工知能）のアルゴリズムによってタイプした文字に変換される。

■若かりし日の自分に「良くなるから」
　「Ｔ５」は徐々に、文章を写す作業では１分間に９０文字（約１８単語）、質問に答える作業では１分間に７４文字（約１５単語）を打ち出すことができるようになった。
　カーソルの「ポイント・クリック」によるシステムで生み出せる文字数は、１分間当たり最大４０文字だ。
　エラーについても、スマートフォンにあるようなオートコレクト機能を追加すれば、１～２％に削減できると論文著者らは言う。
　ただ、研究対象は１人だけであり、また、年齢の進行に伴う脳活動の変化にチップがどう適応するかの研究も必要だ。
　ウィレット氏はこれらの課題を認識しつつも、この技術が「数十年以内ではなく、数年以内」に実用化できるとの希望を持っている。
　訓練を積むことで、「Ｔ５」は心に訴えるような思いを表現する機会を得ることができた。例えば、若かりし日の自分に対する助言だ。
　「辛抱強く待て。良くなるから」【翻訳編集ＡＦＰＢＢＮｅｗｓ】

〔ＡＦＰ＝時事〕（2021/05/18-13:55）

Paralysed from the neck down, the man stares intently at a screen. As he imagines handwriting letters, they appear before him as typed text thanks to a new brain implant.
The 65-year-old is typing at a speed similar to his peers tapping on a smartphone, using a device that could one day help paralysed people communicate quickly and easily.
The research could benefit people suffering spinal cord injuries, strokes or motor neurone disease, said Frank Willett, a research scientist at Stanford University and lead author of the study published Wednesday in the journal Nature.
Imagine if you could only move your eyes up and down but couldn't move anything else -? a device like this could enable you to type your thoughts at speeds that are comparable to that of normal handwriting or typing on a smartphone, he told AFP.
Existing devices for those with paralysis rely on eye movement or imagining moving a cursor to point and click on letters.
But Willett and his team wondered whether thinking about handwriting letters might be another way for people to express themselves.
The theory was not necessarily obvious, as handwriting is a much more complex action than moving a cursor from point to point.
But the researchers found that handwriting generates distinctive brain activity that proved easier for an implant to detect and a computer programme to interpret and translate into text.
The research involved a man nicknamed T5 who was paralysed from the neck down after a spinal cord injury in 2007.
He was fitted with two aspirin-sized brain-computer interface (BCI) chips on the left side of his brain that could detect neurons firing in the motor cortex that governs hand movement.
Sensors transmitted the signals to a computer for translation by an artificial intelligence algorithm into typed text.
The first step was to determine whether T5 even produced distinctive and readable brain activity when imagining writing, given the many years since his injury.
And once that activity was detected, the algorithm had to be trained to recognise and interpret the thoughts, a process that took nine days over a six-week period.
T5 painstakingly imagined handwriting individual letters and copying out sentences so the programme could identify which brain activity patterns indicated which letter.
- 'It will get better' -
Over time, T5 was able to produce 90 characters or about 18 words a minute when copying sentences, and around 74 characters or 15 words a minute when replying to questions.
That compares with the maximum 40 characters a minute that point and click systems can produce.
The sentences weren't flawless, with a mistake in about one in every 18 characters when copying and one in every 11 characters when replying to questions.
But adding an autocorrect function like that on a smartphone reduced the error rate to between one and two percent, the authors said.
And even the training exercise offered a chance for T5 to express some poignant thoughts, including the advice he would give his younger self.
Be patient it will get better, he replied.
Writing in a review commissioned by Nature, Pavithra Rajeswaran and Amy Orsborn of the University of Washington's bioengineering department called the work a milestone.
The authors' approach has brought neural interfaces that allow rapid communication much closer to a practical reality, they wrote.
But they cautioned that further testing and refinement is still needed.
The study involved a single participant, and research is needed on how the implant will adapt to the way brain activity changes with age.
Willett acknowledged the challenges, which also include creating technology smart enough to recognise handwriting without training and making the entire set up wireless.
Here, we are just showing a proof-of-concept demonstration that a handwriting BCI is an exciting and potentially viable approach for restoring communication to people who are severely paralysed, he said.
But he is hopeful the technology could be feasible for general use within years as opposed to decades.