What was the air date of the episode with the production code of 322?
CREATE TABLE "table1_2818164_4" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" real
);
SELECT "original_air_date" FROM "table1_2818164_4" WHERE "production_code"=322;