Air carrier Captain reported a fume event during final descent which had a serious physiological affect on flight crew's clear thinking and coordination during landing. Captain debriefed with maintenance after a safe arrival and stated the fogginess was temporary.

Narrative

Flight encountered heavy fumes event below 10;000 feet all the way to parking aircraft and shutting down the engines. The smell was overwhelming and similar to dirty socks or mildew. There was a noticeable change in my thoughts from a relaxed and reactively mindset to a distracted; intense and concerned state.Due to our proximity to airport and the fact that we were being vectored to final approach; we did not reference any manuals. Landing the aircraft immediately was my focus. We did attempt to limit the infusion of fumes by turning off Pack 1. That did not make any noticeable difference. We then turned Pack One on and turned off Pack Two. That did not make any noticeable difference. We then turned on Pack Two. Prior to landing; I believe both pilots were responding at a different rate than normal. At one point I called for flaps or landing gear and did not received a response from the First Officer. When I looked over at him; his eyes were closed. I repeated the command and he opened his eyes and did the required task. Shortly afterward; Approach Control ordered a frequency change. The First Officer responded by moving his hand and pulling the transmit button and making the read back; however his hand was not on the side stick. I told him and he then repeated the callback normally. We landed shortly afterward. On the way to the gate; the First Officer seemed to be operating much slower and appeared slightly confused on during our short taxi to the gate.After arriving at the gate; there was a temporary fogginess to my thoughts. Everything I did had a slower and sloppier feel to it. I had to concentrate much more in order to accomplish routine things. The mechanic told me there were 'several' write ups in the logbook for fume events. I was not aware of this. The [Operations Control] Duty Chief told me that there were no write ups in the last 25 flight cycles. I've heard that over servicing of oil can create fumes events; so it might be important to note that a weekly inspection was accomplished prior to our flight.After leaving the aircraft; I ate some food and drank a lot of water. The fogginess seemed to lift after a period of time. The First Officer also ate some food and appeared to recover his normal level of alertness.