It was a very pleasant start to the trading week for most ASX shares yesterday. Monday's session saw the All Ordinaries (ASX: XAO) Index rise by a confident 0.74% to back over 8,470 points. But let's talk about what was going on with BrainChip Holdings Ltd (ASX: BRN) shares.

The BrainChip share price had a blowout yesterday. The ASX artificial intelligence (AI) stock closed at 23 cents a share last week. But yesterday, those same shares opened at 24 cents before pushing as high as 28 cents, which is where the company managed to close at, a gain worth a huge 21.74%.

Yesterday's epic share price gain was just the latest in what has been an extraordinary run for Bainchip shares of late.

It was only last month that BrainChip was touching a new 52-week low of 14.5 cents a share. But since 18 September, this AI stock is now up a whopping 73.1%. Over just the past fortnight, the company is sitting on a 62.9% rise.

Why have BrainChip shares blown their lid off?

So many investors and watchers of this AI stock might be wondering why Brianchip has blown its lid off over the past month or so. After all, BrainChip hasn't exactly been a winner until recently, with the stock losing a painful 67% or so between February and mid-September.

Well, it's a bit of a mystery, unfortunately. We haven't had any major news out of BrainChip since the company posted its half-year earnings results back on 26 August.

As we covered at the time, these results weren't exactly a delight for investors. Brainchip revealed that its revenues from continuing operations fell 8% over the six months to 30 June to just US$106,693.

That drove a net loss for the company of US$11.52 million, which was an improvement from the US$17.15 million loss from the prior period.

BrainChip also revealed that its cash and cash equivalents fell from US$134.3 million to US$10.9 million over the period.

On the day these results came out, BrainChip shares dropped 7.7%. The company continued to fall all the way through to mid-September. But since then, investors seemed to have decided that BrainChip shares were too cheap to ignore.

This is one possible explanation as to why this company has surged so significantly in value. Perhaps some other value investors decided that it was time to pile back in. Or perhaps a large investor has been buying up shares and pushing the price up.

Unfortunately, there's not enough public information to make a decisive call here. All we know is that it has been a great month to own BrainChip shares. Let's see what happens next.